What Is switch–case in C?

The switch statement is a multi-way branch. Based on the value of an expression, it jumps directly to the matching case block.

You can think of it like a rotary selector switch on a panel: position 1 activates one circuit, position 2 activates another, and so on. In C, the switch statement selects one block of code depending on the value.

Basic Syntax

switch (expression) {
    case constant1:
        // statements for option 1
        break;

    case constant2:
        // statements for option 2
        break;

    case constant3:
        // statements for option 3
        break;

    default:
        // statements if no case matches
}

• expression is evaluated once.
• Its value is compared with constant1, constant2, etc.
• If a match is found, that case block executes.
• break stops the execution and exits the switch.
• default is optional, and runs when no case matches.

Simple switch–case Example

Let’s start with a small example that prints the day name based on a number.

#include <stdio.h>

int main() {
    int day;

    printf("Enter day number (1-3): ");
    scanf("%d", &day);

    switch (day) {
        case 1:
            printf("Monday\\n");
            break;

        case 2:
            printf("Tuesday\\n");
            break;

        case 3:
            printf("Wednesday\\n");
            break;

        default:
            printf("Invalid day\\n");
    }

    return 0;
}

If the user enters 2, the program prints Tuesday. If the user enters 10, none of the cases match, so default is executed.

switch–case vs else-if Ladder

You can write the previous program using an else-if ladder:

if (day == 1) {
    printf("Monday\\n");
} else if (day == 2) {
    printf("Tuesday\\n");
} else if (day == 3) {
    printf("Wednesday\\n");
} else {
    printf("Invalid day\\n");
}

Both versions work, but:

• switch is cleaner when you are checking the same variable against different constant values.
• Many menu programs naturally map to a switch structure.
• For ranges and complex conditions (e.g., x > 10 && x < 50) you should still use if / else-if.

Menu Program Using switch–case

Menu-style programs are very common in real systems: billing apps, control panels, test programs, and embedded device UIs. Let’s build a simple calculator menu.

#include <stdio.h>

int main() {
    int choice;
    float a, b, result;

    printf("=== Simple Calculator ===\\n");
    printf("1. Add\\n");
    printf("2. Subtract\\n");
    printf("3. Multiply\\n");
    printf("4. Divide\\n");
    printf("Enter your choice (1-4): ");
    scanf("%d", &choice);

    printf("Enter two numbers: ");
    scanf("%f %f", &a, &b);

    switch (choice) {
        case 1:
            result = a + b;
            printf("Result = %.2f\\n", result);
            break;

        case 2:
            result = a - b;
            printf("Result = %.2f\\n", result);
            break;

        case 3:
            result = a * b;
            printf("Result = %.2f\\n", result);
            break;

        case 4:
            if (b != 0) {
                result = a / b;
                printf("Result = %.2f\\n", result);
            } else {
                printf("Error: Division by zero!\\n");
            }
            break;

        default:
            printf("Invalid choice!\\n");
    }

    return 0;
}

This example clearly shows the power of switch–case for menu logic: the structure is compact, readable and easy to extend with new options.

Real Life switch–case Examples for Technicians

As a technician, you often deal with modes, fault codes and settings. These map extremely well to switch–case in C.

switch (mode) {
    case 0:
        printf("System OFF\\n");
        // turn off all outputs
        break;

    case 1:
        printf("System in STANDBY\\n");
        // minimal power, ready to start
        break;

    case 2:
        printf("System RUNNING\\n");
        // enable full operation
        break;

    default:
        printf("Unknown mode!\\n");
}

switch (faultCode) {
    case 1:
        printf("Fault 1: Over voltage\\n");
        break;

    case 2:
        printf("Fault 2: Over current\\n");
        break;

    case 3:
        printf("Fault 3: Over temperature\\n");
        break;

    default:
        printf("Unknown fault code\\n");
}

3. Multimeter Function Selector

A digital multimeter might have modes like Voltage, Current, Resistance, Continuity. For a simple simulator program:

char mode;

printf("Select mode (V/I/R/C): ");
scanf(" %c", &mode);

switch (mode) {
    case 'V':
    case 'v':
        printf("Voltage measurement mode\\n");
        break;

    case 'I':
    case 'i':
        printf("Current measurement mode\\n");
        break;

    case 'R':
    case 'r':
        printf("Resistance measurement mode\\n");
        break;

    case 'C':
    case 'c':
        printf("Continuity test mode\\n");
        break;

    default:
        printf("Invalid mode\\n");
}

Here, we handle both uppercase and lowercase using fall-through: case 'V': falls through to case 'v':.

break, default and Fall-Through

The break Statement

break is used inside a switch to indicate: “Stop executing this switch and jump to the statement after it.”

If you forget break, the execution will continue into the next case – this is called fall-through. Sometimes this is useful, but often it is a bug.

Intentional Fall-Through

switch (ch) {
    case 'A':
    case 'a':
        printf("You pressed A or a\\n");
        break;

    case 'B':
    case 'b':
        printf("You pressed B or b\\n");
        break;

    default:
        printf("Other key\\n");
}

Here, 'A' falls through to 'a' so both share the same block of code.

The default Case

The default block runs if none of the case labels match. It is similar to the else part of an if-else chain.

default:
    printf("Invalid selection\\n");
    break;    // break is optional in default if it's the last case

Limitations of switch–case

• The expression must be an integer or character type (no float/double).
• Case labels must be constant expressions (like 1, 'A', 10 + 2).
• You cannot check ranges directly (e.g., case x > 10: is not allowed).
• You cannot use strings (char *) directly as case labels in C (unlike some other languages).

Common Mistakes with switch–case

• Forgetting break and accidentally falling into the next case.
• Using non-constant expressions as case labels.
• Trying to use float or double in switch.
• Not handling the default case, causing silent failures for unexpected values.
• Using the same value twice as a case label (this is not allowed; the compiler will complain).

Quick Checklist for switch–case Programs

• Is the switch expression an integer or character type?
• Are all case labels unique constant values?
• Did you add break at the end of each case (unless you really want fall-through)?
• Did you handle unexpected values using a default case?
• For menu programs: did you show the menu clearly before reading the choice?

Practice Ideas for Technicians

1. Service Menu Simulator: Build a menu with options like “1. Read voltage”, “2. Read current”, “3. Read temperature”, “4. Exit”. Use switch to print different dummy readings for each option.
2. Mode Setting Program: Use a character input ('A', 'B', 'C') to select different operation modes and print the mode description.
3. Alarm Priority: Map integer alarm codes (1, 2, 3, 4…) to text like “Low priority”, “Medium priority”, “High priority”.
4. Language Menu: Use switch to print “You selected English”, “You selected Hindi”, etc., based on a numeric or character choice.

Suggested Featured Image Prompt

You can use this prompt in your image generation tool for the thumbnail:

“Flat 16:9 illustration on a clean light background. In the center, a laptop screen shows a C code snippet with a `switch(choice)` structure and `case 1:`, `case 2:`, `case 3:` and `default:` highlighted. On the left side of the image, a vertical menu panel lists options like `1. Add`, `2. Subtract`, `3. Multiply`, `4. Divide`. Colored arrows connect the menu options to the matching `case` blocks in the code. On the right side, a South Indian / Tamil technician character wearing a simple shirt is pointing at the switch–case diagram with a pen. At the top, bold title text: ‘switch–case in C’ and smaller subtitle: ‘Menu Programs & Real Life Examples for Technicians | Tamil Technicians’. Clean vector style, minimal colors, educational look, high quality.”