Switch

In C, the switch case statement provides a structure for supporting several options or conditions to execute a block of code, similar to the if..else-if..else statement. A main difference here, though, is that this statement is much easier to read and write.

However, it can only evaluate one expression or variable at a time.

Syntax

switch(expression) {
  case value1:
    // Enter code here
    break;
  case value2:
    // Enter code here
    break;
  case value_n:
    // Enter code here
    break;
  default:
    // Enter code here
}

Here’s how the switch (aka switch-case) statement works:

1. The switch expression is evaluated only once.
2. The value of the expression will be compared with the values of each case, and if there is a match the corresponding block of code is executed. If there is no code block provided in the case, the control moves on to the next case until it finds one with a code block, and executes the code block there.
3. The break keyword breaks out of the switch block, and does not evaluate any additional statements in the switch. (Without the break, execution would continue with the next case statement.) The program now exits the switch.
4. The code inside the default case is executed if none of the above cases are matched with the resulting value of the expression. This case is optional, and acts just like the else in an if..else-if..else statement. It serves as a “catch-all” case.

The expression or variable’s resulting value must be of an integral or enumerated type. Examples of valid result types for switch-case expressions are int, double, float, and char. (Remember that characters, which have type char, are integral, because they have integer ASCII codes.) This statement will not be valid for expressions or variables that, for example, result in a string value.

Example 1: Evaluating a variable

The following prints out some statements to a student based on a grade they got on a test or quiz.

#include <stdio.h>

int main(){
  char grade = 'B';
  switch(grade){
    case 'A':
      printf("Excellent!\n");
      break;
    case 'B':
    case 'C':
      printf("Good job!\n");
      break;
    case 'D':
      printf("Okay, you passed.\n");
      break;
    case 'F':
      printf("Better try again...\n");
      break;
    default:
      printf("Invalid grade!!!\n");
  }

  printf("Your grade is %c\n", grade);

  return 0;
}

This example will output:

Good job!
Your grade is B

Example 2: Evaluating an expression

The following determines if the addition of two numbers results in either a total of 5 or 4.

#include <stdio.h>

int main(){
  int num1 = 1;
  int num2 = 3;

  switch(num1 + num2){
  case 5:
    printf("The addition of %d and %d results in 5\n", num1, num2);
    break;
  case 4:
    printf("The addition of %d and %d results in 4\n", num1, num2);
    break;
  default:
    printf("The addition of %d and %d does not result in either 4 or 5\n", num1, num2);
  }
  return 0;
}

This example will output:

The addition of 1 and 3 results in 4

Just as aforementioned, a switch-case statement can be used to evaluate the value of not just a variable, but also an expression, as long as the expression results in one value that is either a number or something containing a numerical value.