Types of Programming Language (1)

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Types of Programming Language (1)

• Three types of programming languages
• Machine languages
• Strings of numbers giving machine specific
  instructions
• Example
• 1300042774
• 1400593419
• 1200274027
• Assembly languages
• English-like abbreviations representing
  elementary computer operations (translated via
  assemblers)
• Example
• LOAD BASEPAY
• ADD OVERPAY
• STORE GROSSPAY

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Types of Programming Language (2)

• High-level languages
• Codes similar to everyday English
• Use mathematical notations (translated via
  compilers)
• Example
• grossPay basePay overTimePay

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High Level Languages

• FORTRAN
• Used for scientific and engineering applications
• COBOL
• Used to manipulate large amounts of data still
  used in established business-software
• Pascal
• Designed for the teaching of structured
  programming
• C
• Evolved by Ritchie from two previous programming
  languages, BCPL and B (early 1970s)
• Used to develop UNIX and other modern operating
  systems
• Standardized in 1989 and 1999 into an
  "unambiguous, machine-independent" definition
• Hardware independent (portable)

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The C Program Environment

• Edit
• Preprocess
• Compile
• Link
• Load
• Execute

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A First C Program (1)

• Comments
• Text surrounded by / and / is ignored by
  computer
• Used to describe program
• include ltstdio.hgt
• Preprocessor directive
• Tells computer to load contents of a certain file
• ltstdio.hgt allows standard input/output operations

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A First C Program (2)

• int main()
• The keyword main indicates where the program
  starts executing
• Parenthesis ( ) always follow the word main
• int means that main "returns" an integer value
  (more on this later!)
• Braces ( and ) indicate a block of code
• The body of main must be contained in braces

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A First C Program (3)

• printf( "Welcome to C!\n" )
• Instructs computer to perform an action
• Specifically, prints the string of characters
  within quotes (" ")
• Entire line called a statement
• All statements must end with a semicolon ()
• Escape character (\)
• Indicates that printf should do something out of
  the ordinary
• \n is the newline character
• return 0
• Indicates the end of the main function

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Compiling and Executing (5)
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An Alternative First C Program

• Produces the same output as the previous program
• Another variation printf(Welcome\nto\nC!\n)
  would produce three lines of output, with
  newlines inserted after the words welcome and to,
  as well as at the end.

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Adding two Numbers (Program Listing)
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Adding two Numbers (New Concepts)

• Lines 13 and 16 read input from the keyboard
• scanf( "d", integer1 )
• scanf( "d", integer2 )
• Lines 8 - 10 declare the programs variables
• int integer1
• int integer2
• int sum
• Line 18 performs a mathematical calculation on
  the numbers input from the keyboard
• sum integer1 integer2
• Line 20 prints to the screen the result of this
  calculation
• printf( "Sum is d\n", sum )

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Adding two Numbers (Discussion)

• As before
• Comments, include ltstdio.hgt and main
• int integer1, integer2, sum
• Definition of variables
• Variables locations in memory where a value can
  be stored
• int means the variables can hold integers (e.g.
  -1, 3, 0, 47)

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Adding two Numbers (Discussion)

• Variable names (identifiers)
• integer1, integer2, sum
• Identifiers consist of letters, digits (cannot
  begin with a digit) and underscores( _ )
• Case sensitive
• Definitions appear before executable statements
• If an executable statement references and
  undeclared variable it will produce a syntax
  (compiler) error

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Adding two Numbers (Discussion)

• scanf( "d", integer1 )
• Obtains a value from the user
• scanf uses standard input (usually keyboard)
• This scanf statement has two arguments
• d - indicates data should be a decimal integer
• is confusing in beginning for now, just
  remember to include it with the variable name in
  scanf statements
• When executing the program the user responds to
  the scanf statement by typing in a number, then
  pressing the enter (return) key

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Adding two Numbers (Discussion)

• (assignment operator)
• Assigns a value to a variable
• Is a binary operator (has two operands)
• sum integer1 integer2
• sum gets the result of integer1 integer2
• Variable receiving value on left
• printf( "Sum is d\n", sum )
• Similar to scanf
• d means decimal integer will be printed
• sum specifies what integer will be printed
• Calculations can be performed inside printf
  statements
• printf( "Sum is d\n", integer1 integer2 )
• Write down some sample screen output that you
  would expect to see when the program is run

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Adding two Numbers (Output)

• This shows an example of what you see when you
  run this program

Enter first integer45 Enter second
integer72 Sum is 117