Structured Program Development

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Structured Program Development

• Dilshad M. Shahid
• New York University
• _at_1998

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Today

• Float Variables
• How to use Borland
• Equality and Relational Operators
• Algorithms
• Pseudocode
• Control Structures

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Float variables

• Float Data Type Data Type that can hold numbers
  with decimal values e.g. 5.14, 3.14
• Float example

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• / Float Example Program /
• include ltstdio.hgt
• main ()
• float var1, var2, var3, sum
• var1 87.25
• var2 92.50
• var3 96.75
• sum var1 var2 var3
• printf(Sum .2f, sum)
• getchar()

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How to use Borland C

• Borland comes with 3 disks. Please use the 5.0
  disk.
• ACF labs have correct version installed
• A new text page automatically when you open
  Borland
• Alternatively, you can go to menu option File,
  then New, then Text Edit

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More Borland

• Use Save As to save to your disk on the A\ drive
• After you type in your program, there are 3 ways
  to compile
• click lightning bolt
• go to menu option Debug, then Run
• Hit Control-F9

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Relational and equality operators

• table adapted from Figure 2.12, pg 38
• standard algebraic in C example in C meaning of C
  condition
• Equality x y x is equal to y
• ! x ! y x is not equal to y
• Relational gt gt x gt y x is greater than y
• lt lt x lt y x is less than y
• gt gt x gt y x is greater than or equal to y
• lt lt x lt y x is less than or equal to y

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Algorithms

• Algorithm the procedure for solving a problem
  in terms of
• the actions to be executed
• the order in which these actions are to be
  executed.
• See pages 56 to 57 for a more detailed
  description.

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Pseudocode

• Pseudocode this is simply writing your code in
  ordinary English to help yourself develop an
  algorithm that will be converted into a
  structured C program.
• More examples in the text book

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Control structures

• All programs can be written in terms of only 3
  control structures
• sequence structure
• selection structure
• repetition structure

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Sequence structure

• This is essentially built into C
• Unless directed otherwise, the computer will
  automatically execute C statements one after
  another in the order in which they are written
• This is called sequential execution

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Selection structure

• A selection structure will perform an action
  based on the conditions it receives
• 3 kinds of selection structures in C
• if
• if/else
• switch

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If statement

• Performs indicated action only when condition is
  true otherwise the action is skipped.
• Example in pseudocode
• If bank balance is less than 100
• Print You are below the required minimum

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If statement

• Same example in C
• int balance
• balance 90
• if (balance lt 100)
• printf(You are below the required minimum
  balance\n)
• What will the output be? Change the program so
  that balance 110. What will the output be in
  this case?
• Answer You are below the required minimum
  balance
• No output.

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If/else statement

• Programmer can specify that different actions are
  to be performed when the condition is true than
  when the condition is false

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If/else statement

• Example in pseudocode
• If bank balance is less than 100
• Print You are below the required minimum
• else
• Print You may withdraw money

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If/else statement

• Same example in C
• int balance
• balance 90
• if (balance lt 100)
• printf(You are below the required minimum
  balance\n)
• else
• printf(You may withdraw money\n)
• Make balance equal 120, i.e. greater than 100.
  What will the output be?

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If/else statement

• Another example in C
• int age
• float height
• age 10
• height 5.0
• if (height gt 4.0) / must have 4.0, it is
  float/
• printf(Your height is f\n, height)
• else
• printf(Your age is d\n, age)
• What will output be if height 4.0 ? Does
  changing value of age affect the program output?