if...else statement provides support to control program flow. if statement make decisions based on conditions. It selects an action, if some condition is met. However, there exits situations where you want to make a decision from available choices. For example - select a laptop from available models, select a menu from available menu list etc.

switch...case statement gives ability to make decisions from fixed available choices. Rather making decision based on conditions. Using switch we can write a more clean and optimal code, that take decisions from available choices.

Syntax of switch...case

switch (expression)
​{
    case constant1:
      // statements
      break;
    case constant2:
      // statements
      break;
    .
    .
    .
    default:
      // default statements
}

How does the switch statement work?

The expression is evaluated once and compared with the values of each case label.

• If there is a match, the corresponding statements after the matching label are executed. For example, if the value of the expression is equal to constant2, statements after case constant2: are executed until break is encountered.
• If there is no match, the default statements are executed.

If we do not use break, all statements after the matching label are executed.

Rules for working with switch case

• Expression inside switch must evaluate to integer, character or enumeration constant. switch...case only works with integral, character or enumeration constant.
• The case keyword must follow one constant of type evaluated by expression. The case along with a constant value is known as switch label.
• You can have any number of cases.
• Each and every case must be distinct from other. For example, it is illegal to write two case 1 label.
• You are free to put cases in any order. However, it is recommended to put them in ascending order. It increases program readability.
• You can have any number of statement for a specific case.
• The break statement is optional. It transfers program flow outside of switch...case

Flowchart of switch...case statement

Example program of switch case: Simple Calculator

// Program to create a simple calculator
#include <stdio.h>
int main() {
    char operator;
    double n1, n2;
    printf("Enter an operator (+, -, *, /): ");
    scanf("%c", &operator);
    printf("Enter two operands: ");
    scanf("%lf %lf",&n1, &n2);
    switch(operator)
    {
        case '+':
            printf("%.1lf + %.1lf = %.1lf",n1, n2, n1+n2);
            break;
        case '-':
            printf("%.1lf - %.1lf = %.1lf",n1, n2, n1-n2);
            break;
        case '*':
            printf("%.1lf * %.1lf = %.1lf",n1, n2, n1*n2);
            break;
        case '/':
            printf("%.1lf / %.1lf = %.1lf",n1, n2, n1/n2);
            break;
        // operator doesn't match any case constant +, -, *, /
        default:
            printf("Error! operator is not correct");
    }
    return 0;
}

Output

Enter an operator (+, -, *,): *
Enter two operands: 5
10
5 * 10 = 50