Programming Language ? C Tutorial Introduction

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Programming Language ? CTutorial Introduction

• ??????

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Content

• Background
• Getting Started
• IDE (Integrated Development Environment)
• Main Parts of C Programs
• Variables and Arithmetic Expressions
• The for statement
• Symbolic Constants
• Character Input and Output
• Arrays
• Functions
• Character Arrays
• External Variables and Scope

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Programming Language ? CTutorial Introduction

• Background

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Textbooks

1. C How to Program, 5th Edition, by Harvey M.
   Deitel , Paul J. Deitel.
2. The C programming Language, 2nd Editon, by Brian
   W. Kernighan and Dennis M. Ritchie, Prentice-Hall
   in 1988.

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Grading

1. Programming 50
2. Midterm 25
3. Final 25

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The C Language

• Currently, the most commonly-used language for
  embedded systems
• High-level assembly
• Very portable
• compilers exist for virtually every processor
• Easy-to-understand compilation
• Produces efficient code
• Fairly concise

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C History
The Development of the C Language

• Developed between 1969 and 1973 along with Unix
• Due mostly to Dennis Ritchie
• Designed for systems programming
• Operating systems
• Utility programs
• Compilers
• Filters
• Evolved from B, which evolved from BCPL

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Computer Architecture
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Programming Language ? CTutorial Introduction

• Getting Started

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Setting Program Development Environment
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Setting Program Development Environment
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Setting Program Development Environment
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Setting Program Development Environment
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Setting Program Development Environment
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Setting Program Development Environment
SystemRoot\system32\cmd.exe /K
"F\VS6\VC98\Bin\VCVARS32.BAT"
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Setting Program Development Environment
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Our First C Program ? Hello World
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Our First C Program ? Hello World
include ltstdio.hgt main() printf("hello,
world\n")
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Our First C Program ? Hello World
include information about standard library
include ltstdio.hgt main() printf("hello,
world\n")
define a function called main that received no
argument values
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Our First C Program ? Hello World
include ltstdio.hgt main() printf("hello,
world\n")
define a function called main that received no
argument values
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Our First C Program ? Hello World
include ltstdio.hgt main() printf("hello,
world\n")
statements of main are enclosed in braces
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Our First C Program ? Hello World
include ltstdio.hgt main() printf("hello,
world\n")
main calls library function printf
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Our First C Program ? Hello World
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Compiling and Linking
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Compiling and Linking
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Compiling and Linking
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Compiling and Linking
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Compiling and Linking
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Compiling and Linking
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Execution
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Execution
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Exercises

1. Create some typo errors for Hello.c, and redo the
   compiling/linking process. Watch and understand
   the screen output reported by cl.
2. Add more printf statements in Hello.c and redo
   the compiling/linking/execution process.

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Programming Language ? CTutorial Introduction

• IDE

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Visual C 6.0
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Visual C 6.0
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Visual C 6.0
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Win32 Console Application
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Win32 Console Application
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Win32 Console Application
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Hello_IDE
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Hello_IDE
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Hello_IDE
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Hello_IDE
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Hello_IDE
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Hello_IDE
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Hello.c
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Building Application
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Building Application
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Execution
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Execution
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Files Generated by IDE
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Programming Language ? CTutorial Introduction

• Main Parts of C Programs

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Main Parts

• Headers/Comments/Expressions

include ltstdio.hgt / Our first C Program
/ main() printf("hello, world\n")
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Example Identify the three parts in the following
program
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Remark
C also uses // to comment a single line.
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The Syntax of C Language
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Programming Language ? CTutorial Introduction

• Variables and Arithmetic Expressions

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ExampleFahrenheit-Celsius table
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ExampleFahrenheit-Celsius Table
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
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ExampleFahrenheit-Celsius Table
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
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Statements
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
Individual statements are terminated by
semicolons.
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Variable Declarations
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step

• In C, all variables must be declared before they
  are used.
• Usually declared at the beginning of the function
  before any executable statements.
• A declaration announces the properties of
  variables it consists of a name and a list of
  variables.

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Variable Declarations

• The integer data type.
• What is its range?

include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
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Integer
int fahr, celsius int lower, upper, step

• The range of integer depends on machine
• 16-bit machine
• ?32768 ? 32767
• 32-bit machine
• ?2147483646 ? 2147483647

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Integer
int fahr, celsius int lower, upper, step

• The range of integer depends on machine

INT_MIN ? INT_MAX
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Integer
int fahr, celsius int lower, upper, step

• The range of integer depends on machine

INT_MIN ? INT_MAX
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Float
float fahr, celsius float lower, upper, step

• A float number is typically a 32-bit quantity,
  with at least six significant digits and
  magnitude generally between about 10-38 and 1038

FLT_MIN ? FLT_MAX
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Fundamental Types
Type Size
char 1 byte
short 2 bytes
int 4 bytes
long 4 bytes
float 4 bytes
double 8 bytes
Machine Dependent
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Fundamental Types in Microsoft C
Type Size
char 1 byte
short 2 bytes
int 4 bytes
long 4 bytes
float 4 bytes
double 8 bytes
Type Size
char 1 byte
short 2 bytes
int 4 bytes
long 4 bytes
float 4 bytes
double 8 bytes
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Assignment Statements
Assign a value computed from an expression to a
variable.
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
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While Loop
while( cond_expression )statement
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
The body of a while loop is repeatedly executed
as long as the condition expression is tested
true.
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Arithmetical Operations
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
Can it be celsius 5/9(fahr-32)? Why?
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printf ? General-Purpose Output Formatting
Function
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
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printf ? General-Purpose Output Formatting
Function
format string
printf("d\td\n", fahr, celsius)
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printf ? General-Purpose Output Formatting
Function
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("d\td\n", fahr, celsius) fahr fahr
step
Left aligned
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printf ? General-Purpose Output Formatting
Function
Synopsis include ltstdio.hgtint printf(const
char format, ...) Description printf writes
to the standard output stream using putchar,
under control of the string pointed to by format
that specifies how subsequent arguments are
converted for output. If there are insufficient
arguments for the format, the behavior is
undefined. If the format is exhausted while
arguments remain, the excess arguments are
evaluated but are otherwise ignored. printf
returns number of characters transmitted, or a
negative value if an output or encoding error
occurred.
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printf ? General-Purpose Output Formatting
Function
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() int fahr, celsius int lower, upper,
step lower 0 / lower limit of temperature
scale / upper 300 / upper limit / step
20 / step size / fahr lower while (fahr
lt upper) celsius 5 (fahr-32) /
9 printf("3d 6d\n", fahr, celsius) fahr
fahr step
Right aligned
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ExampleFahrenheit-Celsius Table (Float)
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
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ExampleFahrenheit-Celsius Table (Float)
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
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More on printf
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Statements

• Simple Statements
• lower 0
• upper 300
• step 20
• fahr lower
• Null Statement
• // a null statement
• Compound Statements
• celsius (5.0/9.0) (fahr-32.0)
• printf("3.0f 6.1f\n", fahr, celsius)
• fahr fahr step

4 simple statements
1 compound statement
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While Statements
while( cond_expression ) statement
a simple statement a null statement a compound
statements
The statement can be
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Program Indentation
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
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Program Indentation
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
Statement
Statement
Statement
Statement
Statement
Statement
Statement
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Program Indentation
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
Statement
Statement
Statement
Statement
Statement
Statement
Statement
Statement
Statement
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Program Indentation
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
Statement
Statement
Statement
Statement
Statement
Statement
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Programming Language ? CTutorial Introduction

• The for Statement

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ExampleFahrenheit-Celsius Table
include ltstdio.hgt / print Fahrenheit-Celsius
table for fahr 0, 20, ..., 300
/ main() float fahr, celsius float lower,
upper, step lower 0 / lower limit of
temperature scale / upper 300 / upper limit
/ step 20 / step size / fahr
lower while (fahr lt upper) celsius
(5.0/9.0) (fahr-32.0) printf("3.0f 6.1f\n",
fahr, celsius) fahr fahr step
There are many ways to do the same task.
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ExampleFahrenheit-Celsius Table
include ltstdio.hgt / print Fahrenheit-Celsius
table / main() int fahr for (fahr 0 fahr
lt 300 fahr fahr 20) printf("3d 6.1f\n",
fahr, (5.0/9.0)(fahr-32))
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The for Statement
include ltstdio.hgt / print Fahrenheit-Celsius
table / main() int fahr for (fahr 0 fahr
lt 300 fahr fahr 20) printf("3d 6.1f\n",
fahr, (5.0/9.0)(fahr-32))
for ( init-exp cond-exp loop-exp ) statement
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for vs. while

• The choice between while and for is arbitrary,
  based on which seems clearer.
• The for is usually appropriate for loops in which
  the initialization and increment are single
  statements and logically related.

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Exercises

1. Modify the temperature conversion program to
   print the table in reverse order, that is, from
   300 degrees to 0.

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Exercises

1. Using only the techniques you learned, write a
   program that calculates the squares and cubes of
   the number from 0 to 10 and used tabs to print
   the following table of values.

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Programming Language ? CTutorial Introduction

• Symbolic Constants

95
define ? Text Substitution
define name replacement list
Example
define PI 3.1415926
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ExampleFahrenheit-Celsius Table
include ltstdio.hgt define LOWER 0 / lower
limit of table / define UPPER 300 / upper
limit / define STEP 20 / step size / /
print Fahrenheit-Celsius table / main() int
fahr for (fahr LOWER fahr lt UPPER fahr
fahr STEP) printf("3d 6.1f\n", fahr,
(5.0/9.0)(fahr-32))
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Programming Language ? CTutorial Introduction

• Character
• Input and Output

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getchar() putchar()
define EOF (-1)
Synopsis include ltstdio.hgt int
getchar(void) Description getchar reads a
single character from the standard input
stream. If the stream is at end-of-file or a read
error occurs, getchar returns EOF.
Synopsis include ltstdio.hgt int putchar(int
c) Description putchar writes the character c
to the standard output stream. putchar returns
the character written. If a write error occurs,
putchar returns EOF.
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Example Typewriter (Version 1)
! not equal
include ltstdio.hgt / copy input to output 1st
version / main() int c c
getchar() while (c ! EOF)
putchar(c) c getchar()
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Example Typewriter (Version 2)
The return value of an assignment statement is
value of the variable after the assignment.
include ltstdio.hgt / copy input to output 2st
version / main() int c c
getchar() while ((c getchar()) !
EOF) putchar(c)
simple statement
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Example Typewriter (Version 2)
The return value of an assignment statement is
value of the variable after the assignment.
include ltstdio.hgt / copy input to output 2st
version / main() int c c
getchar() while ((c getchar()) ! EOF)
putchar(c)
102
Example Character Counting (Version 1)
increment
include ltstdio.hgt / count characters in input
1st version / main() long nc nc
0 while (getchar() ! EOF) nc printf("ld\
n", nc)
simple statement
103
Example Character Counting (Version 1)
increment
include ltstdio.hgt / count characters in input
1st version / main() long nc nc
0 while (getchar() ! EOF) nc printf("ld\n"
, nc)
104
Example Character Counting (Version 2)
include ltstdio.hgt / count characters in input
2nd version / main() double nc for
(nc 0 getchar() ! EOF nc)
printf(".0f\n", nc)
null statement
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Example Character Counting (Version 2)
include ltstdio.hgt / count characters in input
2nd version / main() double nc for
(nc 0 getchar() ! EOF nc)
printf(".0f\n", nc)
106
Example Line Counting
equals to
include ltstdio.hgt / count lines in input
/ main() int c, nl nl 0 while
((c getchar()) ! EOF) if (c '\n')
nl printf("d\n", nl)
if ( expression ) statement if ( expression )
statement else statement
simple statement
107
Example Line Counting
include ltstdio.hgt / count lines in input
/ main() int c, nl nl 0 while
((c getchar()) ! EOF) if (c '\n')
nl printf("d\n", nl)
simple statement
108
Example Line Counting
include ltstdio.hgt / count lines in input
/ main() int c, nl nl 0 while
((c getchar()) ! EOF) if (c '\n')
nl printf("d\n", nl)
Can we move to here?
simple statement
109
Example Word Counting
OIIIIOIIOIOOOIIIIO OIIIII
110
Example Word Counting
include ltstdio.hgt define IN 1 / inside a
word / define OUT 0 / outside a word / /
count lines, words, and characters in input
/ main() int c, nl, nw, nc, state
state OUT nl nw nc 0 while ((c
getchar()) ! EOF) nc if (c '\n')
nl if (c ' ' c '\n' c '\t')
state OUT else if (state OUT) state
IN nw printf("d d
d\n", nl, nw, nc)
111
Exercises

1. Write a program to print a histogram of the
   frequencies of different characters in its input.

112
Programming Language ? CTutorial Introduction

• Arrays

113
Arrays
score
Array is a data structure that stores contiguous
data elements of the same type.
address
distance
Examples
int score50 char address50 double
distance50
114
Arrays
Examples
int score50 char address50 double
distance50
score
address
distance
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Arrays
Examples
int score50 char address50 double
distance50
score
address
distance
116
Arrays
Examples
int score50 char address50 double
distance50
score
address
distance
117
Example Digit Counting
logical and operator
logical or operator
include ltstdio.hgt / count digits, white space,
others / main() int c, i, nwhite,
nother int ndigit10 nwhite nother
0 for (i 0 i lt 10 i) ndigiti
0 while ((c getchar()) ! EOF) if (c gt
'0' c lt '9') ndigitc-'0' else if (c
' ' c '\n' c '\t') nwhite else
nother printf("digits ") for (i 0 i lt
10 i) printf(" d", ndigiti) printf(",
white space d, other d\n", nwhite,
nother)
118
Example Digit Counting
include ltstdio.hgt / count digits, white space,
others / main() int c, i, nwhite,
nother int ndigit10 nwhite nother
0 for (i 0 i lt 10 i) ndigiti
0 while ((c getchar()) ! EOF) if (c gt
'0' c lt '9') ndigitc-'0' else if (c
' ' c '\n' c '\t') nwhite else
nother printf("digits ") for (i 0 i lt
10 i) printf(" d", ndigiti) printf(",
white space d, other d\n", nwhite,
nother)
119
Example Digit Counting
include ltstdio.hgt / count digits, white space,
others / main() int c, i, nwhite,
nother int ndigit10 nwhite nother
0 for (i 0 i lt 10 i) ndigiti
0 while ((c getchar()) ! EOF) if (c gt
'0' c lt '9') ndigitc-'0' else if (c
' ' c '\n' c '\t') nwhite else
nother printf("digits ") for (i 0 i lt
10 i) printf(" d", ndigiti) printf(",
white space d, other d\n", nwhite,
nother)
120
Example Digit Counting
include ltstdio.hgt / count digits, white space,
others / main() int c, i, nwhite,
nother int ndigit10 nwhite nother
0 for (i 0 i lt 10 i) ndigiti
0 while ((c getchar()) ! EOF) if (c gt
'0' c lt '9') ndigitc-'0' else if (c
' ' c '\n' c '\t') nwhite else
nother printf("digits ") for (i 0 i lt
10 i) printf(" d", ndigiti) printf(",
white space d, other d\n", nwhite,
nother)
121
if Statement
The dangling else problem
if (condition1) statement1 else if (condition2)
statement2 else if (condition3)
statement3 ... else statementn
122
Exercises

1. Write a program that prints its input one word
   per line.
2. Write a program that prints only a single white
   character between words.

123
Exercises

1. Write a program to print a histogram of the
   frequencies of different characters in its input.

124
Programming Language ? CTutorial Introduction

• Functions

125
Functions we have used

• printf
• getchar
• putchar

126
Functions

• A way to encapsulate some computation.
• Similar to a subroutine or function in Fortran,
  or a procedure or function in Pascal.
• A properly designed function allow us to
• know what is done, but
• ignore how a job is done

127
Function Definition
return-type function-name(parameter declarations,
if any) declarations statements
128
Function Definition
If absent, return type is considered int.
return-type function-name(parameter declarations,
if any) declarations statements
Called formal parameters
129
Example Power
include ltstdio.hgt int power(int m, int n) /
test power function / main() int i
for (i 0 i lt 10 i) printf("d d
d\n", i, power(2,i), power(-3,i)) return
0 / power raise base to n-th power n gt 0
/ int power(int base, int n) int i, p
p 1 for (i 1 i lt n i) p p
base return p
? forward reference
130
Example Power
include ltstdio.hgt int power(int m, int n) /
test power function / main() int i
for (i 0 i lt 10 i) printf("d d
d\n", i, power(2,i), power(-3,i)) return
0 / power raise base to n-th power n gt 0
/ int power(int base, int n) int i, p
p 1 for (i 1 i lt n i) p p
base return p
131
Example Power (Version 2)
/ power raise base to n-th power n gt 0
version 2 / int power(int base, int n)
int i, p for (p 1 n lt 0 --n) p p
base return p
/ power raise base to n-th power n gt 0
/ int power(int base, int n) int i, p
p 1 for (i 1 i lt n i) p p
base return p
132
Example Power (Version 2)
/ power raise base to n-th power n gt 0
version 2 / int power(int base, int n)
int i, p for (p 1 n lt 0 --n) p p
base return p
. . . . . . . . . . main() int n, val
n 5 val power(2, n)
printf("vald nd d\n", val, n) . . . . . .
. . . .
n?
133
Call by Value

• In C, all function arguments are passed by
  value.
• the called function is given the values of its
  arguments in temporary variables rather than the
  originals.
• Modifying the values of formal parameters doesnt
  effect the value of originals
• How about if a function has arrays as its
  parameters?

134
Programming Language ? CTutorial Introduction

• Character Arrays

135
Strings in C

• Null-terminated string ? In C, a string is stored
  as an array of characters containing the
  characters in the string and terminated with a
  '\0' to mark the end.

str
Example
char str"hello\n"
136
Strings in C
137
Example Print the Longest Line
while (there's another line) if (it's longer
than the previous longest) (save it)
(save its length) print longest line
138
Example Print the Longest Line
Implement a getline() function which returns the
length of the line read.
while (there's another line) if (it's longer
than the previous longest) (save it)
(save its length) print longest line
Implement a copy() function to save string.
139
Example Print the Longest Line
logical and operator
/ getline read a line into s, return length
/ int getline(char s,int lim) int c,
i for (i0 i lt lim-1 (cgetchar())!EOF
c!'\n' i) si c if (c '\n')
si c i si
'\0' return i
140
Example Print the Longest Line
logical and operator
Simplification
/ getline read a line into s, return length
/ int getline(char s,int lim) int c,
i for (i0 i lt lim-1 (cgetchar())!EOF
c!'\n' i) si c if (c '\n')
si c i si
'\0' return i
si c
si c
141
Example Print the Longest Line
logical and operator
/ getline read a line into s, return length
/ / simplified version / int getline(char
s,int lim) int c, i for (i0 i lt
lim-1 (cgetchar())!EOF c!'\n')
si c if (c '\n') si c
si '\0' return i
142
Example Print the Longest Line
/ copy copy 'from' into 'to' assume to is big
enough / void copy(char to, char from)
int i i 0 while ((toi fromi)
! '\0') i
143
Example Print the Longest Line
include ltstdio.hgt define MAXLINE 1000 /
maximum input line length / int getline(char
line, int maxline) void copy(char to, char
from) / print the longest input line
/ main() int len / current line
length / int max / maximum length
seen so far / char lineMAXLINE / current
input line / char longestMAXLINE / longest
line saved here / max 0 while ((len
getline(line, MAXLINE)) gt 0) if (len gt max)
max len copy(longest, line) if
(max gt 0) / there was a line / printf("s",
longest) return 0 . . . . . . . . . . . .
144
Example Print the Longest Line
145
Example Print the Longest Line
146
Example Print the Longest Line
147
Exercises

1. Write a function getlinestr() by modifying
   getline() described above so that the string read
   doesnt include '\n'.
2. Write a function reverse(char s) that reverses
   the character string s.
3. Write a function int strlen(char s) that
   returns the number of characters in string s.
4. Write a program to demonstrate that the about
   three functions you wrote are correct.

148
Exercises

1. Write a function int atoi(char s) that converts
   a signed decimal numeric string, assumed the
   syntax is correct, to an integer, and write a
   program to verify the correctness of your
   program.
2. Write a program that reads two integers from the
   standard input stream and output their minimum
   and maximum to the standard output stream. You
   cant use library function scanf() to read data.
3. (Take home) Write a function void itoa(int n,
   char s) that converts a signed integer to a
   signed decimal numeric string, and write a
   program to verify the correctness of your program.

149
Programming Language ? CTutorial Introduction

• External Variables and Scope

150
Local (Private) Variables
include ltstdio.hgt define MAXLINE 1000 /
maximum input line length / int getline(char
line, int maxline) void copy(char to, char
from) / print the longest input line
/ main() int len / current
line length / int max / maximum
length seen so far / char lineMAXLINE
/ current input line / char
longestMAXLINE / longest line saved here /
max 0 while ((len getline(line,
MAXLINE)) gt 0) if (len gt max)
max len copy(longest, line)
if (max gt 0) / there was a line
/ printf("s", longest) return 0
/ getline read a line into s, return length
/ / simplified version / int getline(char
s,int lim) int c, i for (i0 i lt
lim-1 (cgetchar())!EOF c!'\n')
si c if (c '\n') si c
si '\0' return i / copy copy
'from' into 'to' assume to is big enough / void
copy(char to, char from) int i i
0 while ((toi fromi) ! '\0') i
151
Local (Private) Variables
include ltstdio.hgt define MAXLINE 1000 /
maximum input line length / int getline(char
line, int maxline) void copy(char to, char
from) / print the longest input line
/ main() int len / current
line length / int max / maximum
length seen so far / char lineMAXLINE
/ current input line / char
longestMAXLINE / longest line saved here /
max 0 while ((len getline(line,
MAXLINE)) gt 0) if (len gt max)
max len copy(longest, line)
if (max gt 0) / there was a line
/ printf("s", longest) return 0
/ getline read a line into s, return length
/ / simplified version / int getline(char
s,int lim) int c, i for (i0 i lt
lim-1 (cgetchar())!EOF c!'\n')
si c if (c '\n') si c
si '\0' return i / copy copy
'from' into 'to' assume to is big enough / void
copy(char to, char from) int i i
0 while ((toi fromi) ! '\0') i

• Each local variable comes into existence only
  when the function is called, and disappears when
  the function is exited.
• Hence, also known as automatic variables.

152
Global (Extern) Variables

• Global variables that are defined external to all
  functions can be accessed by name by any
  function.
• Furthermore, they remain in existence permanently.

153
Example Print the Longest Line
include ltstdio.hgt define MAXLINE 1000 /
maximum input line size / int max
/ maximum length seen so far / char
lineMAXLINE / current input line / char
longestMAXLINE / longest line saved here
/ int getline(void) void copy(void) / print
longest input line specialized version
/ main() . . . . . . . . . . . . /
getline specialized version / int
getline(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) . . . . . . . . . . . .
defined external to all functions
154
Example Print the Longest Line
include ltstdio.hgt define MAXLINE 1000 /
maximum input line size / int max
/ maximum length seen so far / char
lineMAXLINE / current input line / char
longestMAXLINE / longest line saved here
/ int getline(void) void copy(void) / print
longest input line specialized version
/ main() . . . . . . . . . . . . /
getline specialized version / int
getline(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) . . . . . . . . . . . .
defined external to all functions
/ print longest input line specialized version
/ main() int len extern int max
extern char longest max 0 while
((len getline()) gt 0) if (len gt max)
max len copy()
if (max gt 0) / there was a line /
printf("s", longest) return 0
155
Example Print the Longest Line
include ltstdio.hgt define MAXLINE 1000 /
maximum input line size / int max
/ maximum length seen so far / char
lineMAXLINE / current input line / char
longestMAXLINE / longest line saved here
/ int getline(void) void copy(void) / print
longest input line specialized version
/ main() . . . . . . . . . . . . /
getline specialized version / int
getline(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) . . . . . . . . . . . .
defined external to all functions
/ getline specialized version / int
getline(void) int c, i extern char
line for (i 0 i lt MAXLINE - 1
(cgetchar()) ! EOF c ! '\n' i)
linei c if (c '\n')
linei c i linei
'\0' return i
156
Example Print the Longest Line
include ltstdio.hgt define MAXLINE 1000 /
maximum input line size / int max
/ maximum length seen so far / char
lineMAXLINE / current input line / char
longestMAXLINE / longest line saved here
/ int getline(void) void copy(void) / print
longest input line specialized version
/ main() . . . . . . . . . . . . /
getline specialized version / int
getline(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) . . . . . . . . . . . .
defined external to all functions
/ copy specialized version / void
copy(void) int i extern char line,
longest i 0 while ((longesti
linei) ! '\0') i
157
Example Print the Longest Line
The declarations for referencing external
variables are redundant if they are defined in
the header part of the same file .
/ print longest input line specialized version
/ main() int len extern int max
extern char longest max 0 while
((len getline()) gt 0) if (len gt max)
max len copy()
if (max gt 0) / there was a line /
printf("s", longest) return 0
include ltstdio.hgt define MAXLINE 1000 /
maximum input line size / int max
/ maximum length seen so far / char
lineMAXLINE / current input line / char
longestMAXLINE / longest line saved here
/ int getline(void) void copy(void) / print
longest input line specialized version
/ main() . . . . . . . . . . . . /
getline specialized version / int
getline(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) . . . . . . . . . . . .
defined external to all functions
/ getline specialized version / int
getline(void) int c, i extern char
line for (i 0 i lt MAXLINE - 1
(cgetchar()) ! EOF c ! '\n' i)
linei c if (c '\n')
linei c i linei
'\0' return i
/ copy specialized version / void
copy(void) int i extern char line,
longest i 0 while ((longesti
linei) ! '\0') i
158
Example Print the Longest Line (Multiple Source
Files) ? I
/ main.c / include ltstdio.hgt define MAXLINE
1000 / maximum input line size / int max
/ maximum length seen so far
/ char lineMAXLINE / current input line
/ char longestMAXLINE / longest line saved
here / int getline(void) void copy(void) /
print longest input line specialized version
/ main() . . . . . . . . . . . .
/ functions.c / / getline specialized
version / int getline(void) . . . . . . .
. . . . . / copy specialized version
/ void copy(void) . . . . . . . . . . . .

159
Example Print the Longest Line (Multiple Source
Files) ? I
/ print longest input line specialized version
/ main() int len extern int max
extern char longest max 0 while
((len getline()) gt 0) if (len gt max)
max len copy()
if (max gt 0) / there was a line /
printf("s", longest) return 0
/ main.c / include ltstdio.hgt define MAXLINE
1000 / maximum input line size / int max
/ maximum length seen so far
/ char lineMAXLINE / current input line
/ char longestMAXLINE / longest line saved
here / int getline(void) void copy(void) /
print longest input line specialized version
/ main() . . . . . . . . . . . .
/ getline specialized version / int
getline(void) int c, i extern char
line for (i 0 i lt MAXLINE - 1
(cgetchar()) ! EOF c ! '\n' i)
linei c if (c '\n')
linei c i linei
'\0' return i
Must be kept.
/ functions.c / / getline specialized
version / int getline(void) . . . . . . .
. . . . . / copy specialized version
/ void copy(void) . . . . . . . . . . . .

/ copy specialized version / void
copy(void) int i extern char line,
longest i 0 while ((longesti
linei) ! '\0') i
Must be kept.
160
Example Print the Longest Line (Multiple Source
Files) ? II
/ main.c / include ltstdio.hgt define MAXLINE
1000 / maximum input line size / int max
/ maximum length seen so far
/ char lineMAXLINE / current input line
/ char longestMAXLINE / longest line saved
here / int getline(void) void copy(void) /
print longest input line specialized version
/ main() . . . . . . . . . . . .
/ externdef.h / define MAXLINE 1000 /
maximum input line size / extern int max
/ maximum length seen so far / extern char
line / current input line / extern char
longest / longest line saved here /
/ functions.c / include ltstdio.hgt include
"externdef.h" / getline specialized version
/ int getline(void) . . . . . . . . . . .
. / copy specialized version / void
copy(void) . . . . . . . . . . . .
161
Example Print the Longest Line (Multiple Source
Files) ? II
/ main.c / include ltstdio.hgt define MAXLINE
1000 / maximum input line size / int max
/ maximum length seen so far
/ char lineMAXLINE / current input line
/ char longestMAXLINE / longest line saved
here / int getline(void) void copy(void) /
print longest input line specialized version
/ main() . . . . . . . . . . . .
/ externdef.h / define MAXLINE 1000 /
maximum input line size / extern int max
/ maximum length seen so far / extern char
line / current input line / extern char
longest / longest line saved here /
/ getline specialized version / int
getline(void) int c, i extern char
line for (i 0 i lt MAXLINE - 1
(cgetchar()) ! EOF c ! '\n' i)
linei c if (c '\n')
linei c i linei
'\0' return i
/ functions.c / include ltstdio.hgt include
"externdef.h" / getline specialized version
/ int getline(void) . . . . . . . . . . .
. / copy specialized version / void
copy(void) . . . . . . . . . . . .
/ copy specialized version / void
copy(void) int i extern char line,
longest i 0 while ((longesti
linei) ! '\0') i
162
Exercise

1. (Take home) Write a program to remove all
   comments from a C program. Don't forget to handle
   quoted strings and character constants properly.
   C comments don't nest.