Counter Controlled loops (for loops in C)

General Information

• One control variable of some integral type (like int)
• One comparison using the control variable (restrict to <, >, <=, or >=)
• Increment or decrement (as appropriate) by a consistent amount
• MAKE NO CHANGES to the loop control variable, the stopping value, or the increment value in the body of the loop
• Loop executes 0 or more times. The number of times it loops can be determined by subtracting the start value from the stop value and after adding 1 to the result, divide it by the increment value.

C specifics

• None of the above rules are enforced by the C language.
• The for loop in C is extremely flexible and can actually take the place of any other loop in the language. However, I expect you to reserve its use to counting from a start to a finish. The examples given here use the loop in the way I want you to use it.
• In fact, if you follow the "rules" listed below, the likelihood of writing an infinite for loop is very small.
• The loop control variable MUST be declared in the declaration section.
• Examples:
  • for i = 1 to 100 by 1 means count from 1 to 100 by 1's (i will start with 1 and that value will be compared to the stopping value. If the comparison is true, the loop executes. After the loop executes, i will be incremented by 1. This continues until i is greater than the stopping value.)
  • for i = 10 to 1 by 2 means count from 10 to 1 by 2's (i will start with 10 and have the subsequent values of 8, 6, 4, 2, 0 at which point the loop will cease to execute. It will NOT execute when the value of i is 0)
  • for i = 7 to 31 by 5 means count from 7 to 31 by 5's (i will have the following values 7, 12, 17, 22, 27, 32)

  ---

  General Outline for a C for loop

  • initialization - set the loop control variable to a starting value
  • comparison - comparison using the loop control variable and the stopping condition
  • increment - increments (decrements) the loop control variable by some constant value

  
       for (initialization; comparison; increment)
         single_statement;
  
  
       for (initialization; comparison; increment)
       {
         statement(s);
       }
  
  

  ---

  Examples of using a for loop to provide a counter controlled loop.

       for (i = 2; i <= 6; i++)
         printf("%d  ",i);
  
       OUTPUT: 2  3  4  5  6
  

  ---

       start = 3;
       finish = 7;
       step = 2;
  
       for (i = start; i < finish;  i = i + step)
         printf("%d  ", i);
  
       OUTPUT: 3 5 
  

  ---

      
       start = 7;
       finish = 3;
       step = 2;
  
       for (i = start; i > finish;  i = i - step)
         printf("%d  ", i);
  
       OUTPUT: 7 5
  

  ---

  Some legal but not good for loops

  C does NOT restrict the for loop to being simply a counter control. It allows the for loop to do everything that a while or do-while loop can. However, you should ONLY use the for loop for counter controlled loops and the while or do-while for logic control. Following are some examples of the poor use of for loops.

  ---

     for (count = 0, temp = 2; ((count < 10)&&(temp > 0)); 
              count += 3, temp--)
        printf("%d %d \n", count, temp);
  
  
     OUTPUT: 0 2
             3 1
  
  Equivalent while
  
     count = 0;
     temp = 2;
     while ((count < 10)&&(temp > 0)) 
     {
        printf("%d %d \n", count, temp);
        count += 3;
        temp--;
     } 
  

  ---

  
     count = 3;
     for (temp = 2; ((count < 10)&&(temp > 0)); count += 3, temp--)
        printf("%d %d \n", count, temp);
  
  
     OUTPUT: 3 2
             6 1
  
  Equivalent while
  
     count = 3;
     temp = 2;
     while ((count < 10)&&(temp > 0))
     {
        printf("%d %d \n", count, temp);
        count += 3; 
        temp--; 
     }
  

  ---

      for (count = 0; count < 5; printf("%d ", count++));
  
  
      OUTPUT: 0 1 2 3 4
  
  Equivalent while
  
      count = 0;
      while (count < 5)
      {
        printf("%d ", count);
        count++;
      }
  

  ---

      for (count = 0; count < 4; )
      {
        printf("%d ", count);
        count = count + 1;
      }
  
      OUTPUT: 0 1 2 3
  
  Equivalent while
  
      count = 0;
      while (count < 4 )
      {
        printf("%d ", count);
        count = count + 1;
      }
  
  

  ---

      count = 0;
      for (; count <= 10; )
      {
        printf("%d ", count);
        count = count + 2;
      }
        
      OUTPUT: 0 2 4 6 8 10
  
  Equivalent while
  
      count = 0;
      while (count <= 10)
      {
        printf("%d ", count);
        count = count + 2;
      }