Switch-case statements: break and default

📖 Theory

The menu problem

The marks program is becoming an app, and apps have menus:

1. View marks

2. View percentage

3. View grade

4. Exit

An if-else ladder can handle it: if choice is 1... else if 2... but it reads like bureaucracy, and every rung re-tests choice.

For "jump straight to MY option", C carries a purpose-built tool: switch-case, along with its two famous sidekicks, break and default.

📖 Theory

The lift, not the staircase

An if-else ladder is a staircase: you pass every floor below yours, answering a question at each. switch is the lift: press 3, arrive at floor 3 directly. But this lift has a quirk: its doors do not close behind you. Unless you press the stop button (break), you walk on into floor 4, then 5... And for buttons that match no floor, the lift has a rescue landing: default.

⌨️ Practical

The marks menu

#include <stdio.h>

int main() {
    int choice, marks = 78;
    printf("1.Marks 2.Percentage 3.Grade : ");
    scanf("%d", &choice);

    switch (choice) {
        case 1:
            printf("Marks: %d\n", marks);
            break;
        case 2:
            printf("Percentage: %.2f\n", marks * 100.0 / 100);
            break;
        case 3:
            printf("Grade: %c\n", marks >= 70 ? 'A' : 'B');
            break;
        default:
            printf("Invalid choice\n");
    }
    return 0;
}

This example runs in Gri-Learn on the web, where you can edit it and see the output.

📖 Theory

The rules of the lift

• switch (expression): the expression must be an integer type (int or char; chars work because they are ASCII numbers). Never float, and never a string.
• case CONSTANT:: labels must be constants: case 1:, case 'A':. A condition like case marks >= 35: is illegal, switch matches VALUES, it does not test ranges.
• break;: exits the switch. Without it, execution falls through into the next case's code, matching stops but running does not.
• default:: runs when nothing matched, C's "none of the above". Position is flexible; the end is convention.

🧩 Quiz

In the menu code, suppose case 1 had NO break. The user enters 1. What prints?

1. Marks AND Percentage: execution falls through into case 2 until its break
2. Only Marks: cases end automatically
3. A compile error: break is compulsory
4. Invalid choice

💭 Think first

Why switch cannot grade

A student tries: switch (marks) { case marks >= 70: ... }. It will not compile. From the lift picture, reason out WHY, and name the right tool for grading.

⚠️ Watch out

Where marks leak

Forgotten breaks: the eternal fall-through, trace every case in predict-the-output questions. switch on a float (switch (percentage)): illegal, integer types only. Conditions as case labels: illegal, constants only. And do not forget default in menu programs; examiners look for invalid-input handling, and it is one line of easy marks.

📖 Theory

Choosing between the two selectors

Your decision toolkit is now complete: ladder for ranges, switch for menus, and both appear together in real programs (a switch menu whose case 3 contains a grading ladder, exactly like today's code). What neither can do is repeat: process 60 students means 60 manual runs. Repetition, the third structured-programming shape, arrives next: while, do-while and for.

✅ Summary

Key takeaways

• switch jumps directly to the case matching an int/char value.
• case labels are constants only: no floats, no conditions, no ranges.
• break exits the switch; without it execution FALLS THROUGH to the next case.
• default catches unmatched values, the none-of-the-above branch.
• switch for exact-match menus; if-else ladder for ranges.
• Memory hook: the lift with doors that never close on their own.