Switch

In C, the switch statement provides a structure for supporting several options or conditions to execute a block of code. It provides a clean and effective alternative to lengthy if-else chains when checking a variable against multiple constant values. It is commonly used when a given variable’s value must be compared against multiple possible options.

Syntax

Here is the syntax for the switch statement (or the switch case):

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

How Switch Case Works

Here’s how the switch statement works:

1. The 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.
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 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. This statement will not be valid for expressions or variables that, for example, result in a string value.

Note: Remember that characters with type char are integral because they have integer ASCII codes.

Switch vs If-Else

Example 1: Evaluating a Variable

This example 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;
}

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This code will output:

Good job!
Your grade is B

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Example 2: Evaluating an Expression

This example 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;
}

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This code will output:

The addition of 1 and 3 results in 4

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Just as aforementioned, a switch 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.

Frequently Asked Questions

1. Can we use strings in switch cases?

No, C does not support switch with strings. It only works with int, char, and enum types.

2. What happens if we forget to add break in switch?

The control will fall through to the next case and execute all subsequent cases until a break or end of switch is encountered.

3. Is default necessary in a switch statement?

No, default is optional in a switch statement. However, it is a good practice to include default to handle unexpected values.

4. Can two cases in switch have the same value?

No, case labels in switch must be unique. Duplicate case values will result in a compilation error.

5. Can we nest switch statements?

Yes, a switch can be nested inside another switch, though this can reduce code clarity and is rarely recommended.