Control statements

Control statements determine the order in which nested statements are executed. In the following, b denotes a boolean expression, i is a variable of any simple type and s, s1 and s2 are single statements. Where more than one statement is required in a control structure, a block should be used.

• IF

     if (b) s1;           // if b is true, s1 is executed
  
     if (b) s1; else s2;  // if b is true, s1 is executed, but
                          // if b is false, s2 is executed
  
     if (b)
     {
        // executed only if b is true
        s1;
        s2;
     }
  
     if (b)
     {
        // executed only if b is true
        s1;
        s2;
     }
     else
     {
        // executed only if b is false
        s3;
        s4;
     }
  

• SWITCH

     switch (i)
     {
        case i1:
           s1;      // s1, s2 executed if i == i1
           s2;
           break;
  
        case i2:
           s3;      // s3 executed if i == i2
           break;
  
        // ... more cases as required
  
        default:
           s4;      // s4 executed only if none of the cases matches
           break;
     }
  

  i1 and i2 are constants of the same type as variable i, which must be an integral type.

• WHILE

     while (b) s1;  // s1 executed repeatedly while b is true
  
     while (b)      // s1, s2 executed repeatedly while b is true
     {
        s1;
        s2;
     }
  

  Note that if b is false, s1 or s1 and s2 will not be executed at all.

• DO...WHILE

     do s1; while (b);    // s1 executed repeatedly until b is false
  
     do                   // s1, s2 executed repeatedly until b is false
     {
        s1;
        s2;
     }
     while (b);
  

  Note that s1 or s1 and s2 are executed at least once (even if b is false).

• FOR

     for (s_initialisation; e_boolean; s_increment)
     {
        s1;
        s2;
     }
  

  is equivalent to (but clearer in intent than):

     s_initialisation;
     while (e_boolean)
     {
        s1;
        s2;
  
        s_increment;
     }
  

  for example:

     for (int i = 0; i < 20; i++)
     {
        s1;      // s1, s2 executed 20 times
        s2;      //   with i = 0 ... i = 19
     }