Loops

1
Loops Functions

• Chapters 10 11

2
Loops

• While
• while(condition) statement
• short i1while( ilt10 ) printf(d\n, i
  ) i
• Do-While
• do statementwhile(condition)
• short i1do printf(d\n, i )
  iwhile( i lt 10 )
• For
• for(initializer condition control) statement
• for( short i0 ilt10 i ) printf(d\n, i )

3
Loop Caveat

• Never use the or ! operators in loops (or
  decisions) with floating point values. Round-off
  error could cause your condition to never be true
  and thus put you in an infinite loop.

4
Functions a.k.a. Subprograms

• The key to writing procedural programs is to
  break up code into small pieces by using
  functions.
• Main reasons for creating many small functions
• Reusability reduces the amount of code you need
  to write if you can repeatedly use the same code.
• Ease of writing testing writing small
  functions takes very little time, and it allows
  you to immediately test the functionality of your
  function. It is much easier to debug code 10
  lines at a time than it is to debug several
  hundred or thousand lines at a time.

5
Rules of Thumb

• Ideally, your functions should be only 10 15
  lines long.
• To increase reusability, functions that could
  possibly be used in the future should be written
  as generic as possible to maximize the number of
  situations they will work in.

6
Writing a function

• In C, functions must be both declared and
  defined.
• A definition contains the function header, and
  the body.
• Definitions dont need to be in a specific place
  or order.
• A declaration (also called a prototype) is a copy
  of the function header placed immediately after
  your include statements and before your main()
  function.
• You must make declarations so the compiler can
  check the syntax of your function calls.
• The main() function doesnt need a declaration.
• Definitions and declarations may both be made in
  two different forms ANSI form, and K R form.
  We will be dealing only with the ANSI form.

7
Function Definition Syntax

• return_type function_name(arguments) body
• An exampleint compute_division(int op1, int
  op2) float result result op1 /
  op2 printf(d/df,op1,op2,result) return
  0

8
Function Declaration Syntax

• return_type function_name(argument types)
• examples
• int compute_division(int, int)
• int compute_division(int op1, int op2)
• In your declarations, you only need to specify
  the argument type, not the variable name it will
  be assigned to since its not needed for syntax
  checking of function calls. You may include the
  variable name if you wish, the compiler will just
  ignore the name. This means you can just copy
  and paste the function header below the include
  section, add a semicolon to the end and youve
  created youre done.

9
Return Types

• Return types must be scalar values. They cannot
  be aggregate types (structs, arrays, etc.)
• You can return a pointer to an aggregate type
  since a pointer is considered scalar.
• You may also use a void return type. It is a
  good practice to always return a value from your
  functions indicating a success or failure.
  Customarily, a value of 0 indicates success. Any
  other value indicates failure.

10
Function Calls Arguments

• Function calls and variable scope work exactly
  the same way in C as they do in Java.
• long i declared in main is different than the
  long i declared in function compute_division
• Arguments in C are passed by value by default.
  This means that only the value of the variable
  being passed is sent to the function. Changes to
  that variable inside of your function will not
  affect the value back in main.
• Arguments may be passed by reference, meaning
  that your functions CAN affect the variables in
  the functions that they were called from through
  the use of pointers. This effectively allows you
  to return an unlimited number of values. Well
  cover this more when we get to the section on
  pointers.

11
Static Variables

• Static variables allow you to preserve the value
  of a variable across function calls.
• Lets assume we have this function
• void test( )
• static long i0
• printf(d\n,i)
• i
• What will be print the first time we call this
  function?
• The second?
• The third?