Pretest Logic controlled loops - While loops

General information

• While loops execute 0 or more times.
• While loops have 1 or more loop control variables.
• The data type of the loop control variable can be any legal type; including float.
• While loops should have at least 1 comparison for each loop control variable.
• Inside the body of the while loop, there should be at least one statement to change a loop control variable. There should be at least one statement for each loop control variable.
• The comparison expressions can be simple (x < 10) or compound ((x < 10) && (x > 0)).
• While loops should be used whenever the code in the body of the loop only needs to execute under certain conditions but may not need to execute at all.

Basic Outline of a while loop.

     while (some expression evaluates to true)
       single_statement;

     while (some expression evaluates to true)
     {
       statement(s);
     }

Examples

  count = 0;
  while (count < 20)
  {
    printf("\n%d ", count);
    count = count + 2;
  }  


  scanf("%d", &count);
  while (count < 20)
  {
    printf("\n%d ", count);
    count = count + 2;
  }



  scanf("%d", &value);
  while (value < 0)
  {
    printf("\nError - try again.  Value must be >= 0");
    scanf("%d", &value);
  }