Control Structures: switch Statements

Switch Statements

The generalized grammar for a switch statement is as follows. First, you must begin with switch, followed directly by a set of parenthesis and an expression that will yield an int value within the parenthesis. Note this could be the result of a mathematical expression or a char value. Why a char value? Recall that a char value has an int representation (its American Standard Code for Information Interchange (ASCII) value). Thus the char will also be viewed as an int. Next, the switch and parenthesis will be followed by a connected statement block, marked by the open and closing pair of curly brackets. The int value within the parenthesis will be compared for equivalence against a series of case value pairs contained within the statement block. Each of the values will be a literal of the type int or char (again where the char is viewed as an int). In addition, note that once an equivalent case value has successfully been found, no more case values will be examined. Simply the statements to the right of the case values will be executed until a break statement is reached or the closing curly bracket is reached. Example syntax is listed here.

Example structure of a switch statement.

 switch (int) {
   case value1:  // the statements to execute if literal 
                 // value1 is equivalent
                 // optionally a break can be listed
   case value2:  // the statements to execute if literal 
                 // value2 is equivalent
                 // optionally a break can be listed

   // ...

   case valueN:  // the statements to execute if literal 
                 // valueN is equivalent
                 // optionally a break can be listed
   default:      // the default statements to execute if
                 // none of the literal values matched
 }

Here is an example code fragment of a switch statement that will print the string value of the digits 0 through 9.

 switch (number) {
   case 0:  printf("zero\n");
            break;
   case 1:  printf("one\n");
            break;
   case 2:  printf("two\n");
            break;
   case 3:  printf("three\n");
            break;
   case 4:  printf("four\n");
            break;
   case 5:  printf("five\n");
            break;
   case 6:  printf("six\n");
            break;
   case 7:  printf("seven\n");
            break;
   case 8:  printf("eight\n");
            break;
   case 9:  printf("nine\n");
            break;
   default: printf("Not 0 through 9\n");
 }

Here is an example code fragment of a switch statement that switches against a char value.

 switch(grade) {
   case 'A':  printf("Exellent\n");
              break;
   case 'B':  printf("Good\n");
              break;
   case 'C':  printf("Average\n");
              break;
   case 'D':  printf("Below Average\n");
              break;
   case 'E':  printf("Failed\n");
              break;
   default:   printf("Invalid\n");
 }

Here is an example code fragment of a switch statement that shows the falling policy to the right of the colon once an equivalent value has been found.

 switch(grade) {
   case 'A':
   case 'B':
   case 'C':  printf("PASS\n");
              break;
   case 'D':
   case 'F':  printf("FAIL\n");
              break;
   default:   printf("Invalid\n");
 }