C language notes

Aman Verma

3 min read

·

Aug 19, 2025

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What is a Switch Statement?

• switch is a selection statement in C.
• It allows us to execute only one case from many cases depending on the value of an expression.
• It works like a ladder if-else, but internally it is faster because it jumps directly to the matching case.

🔹 Rules of Switch

1. Case values must be constant integer or char (no float, no string, no variables).
2. No duplicate cases allowed.
3. Case must end with : (colon).
4. Break is used to stop execution after one case. If not, execution will fall through to the next case.
5. Default works like else (optional).
6. Case values cannot be ranges (like 1..10 not allowed).

Keywords: switch, case, break, default.

🔹 Syntax

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

🔹 5 Good Examples of Switch in C

1. Check Even / Odd

#include <stdio.h>
int main() {
    int n;
    scanf("%d", &n);

    switch(n % 2) {
        case 0:
            printf("%d is Even\n", n);
            break;
        case 1:
            printf("%d is Odd\n", n);
            break;
    }
    return 0;
}

2. Simple Calculator

#include <stdio.h>
int main() {
    int a, b;
    char op;
    scanf("%d %d %c", &a, &b, &op);

    switch(op) {
        case '+': printf("Sum = %d\n", a + b); break;
        case '-': printf("Difference = %d\n", a - b); break;
        case '*': printf("Product = %d\n", a * b); break;
        case '/': printf("Quotient = %d\n", a / b); break;
        default: printf("Invalid Operator\n");
    }
    return 0;
}

3. Day of the Week

#include <stdio.h>
int main() {
    int day;
    scanf("%d", &day);

    switch(day) {
        case 1: printf("Monday\n"); break;
        case 2: printf("Tuesday\n"); break;
        case 3: printf("Wednesday\n"); break;
        case 4: printf("Thursday\n"); break;
        case 5: printf("Friday\n"); break;
        case 6: printf("Saturday\n"); break;
        case 7: printf("Sunday\n"); break;
        default: printf("Invalid Day\n");
    }
    return 0;
}

4. Grade Evaluation

#include <stdio.h>
int main() {
    int marks;
    scanf("%d", &marks);

    switch(marks / 10) {   // divide to get grade range
        case 10:
        case 9: printf("Grade: A\n"); break;
        case 8: printf("Grade: B\n"); break;
        case 7: printf("Grade: C\n"); break;
        case 6: printf("Grade: D\n"); break;
        default: printf("Grade: F\n");
    }
    return 0;
}

5. Menu-Driven Program

#include <stdio.h>
int main() {
    int choice;
    printf("1. Hello\n2. Bye\n3. Exit\n");
    scanf("%d", &choice);

    switch(choice) {
        case 1: printf("Hello User!\n"); break;
        case 2: printf("Goodbye!\n"); break;
        case 3: printf("Exiting...\n"); break;
        default: printf("Invalid Choice\n");
    }
    return 0;
}

✅ These are common real-life uses of switch:

• Mathematical calculations
• Menus in programs
• Checking conditions (like even/odd, days, grades)

second day — — — — — — — — — — — — — — — — — — — — — — — — — — — — —

🔹 Corrected & Modern Version (works in GCC/VS Code)

#include <stdio.h>
#include <stdlib.h>

int main() {
    int qty, op, amt = 0;    while (1) {
        printf("\n**********************************************\n");
        printf("\t\t\t HOTEL SAI BALAJI\n");
        printf("\t\t\t   AMEERPET - HYD\n");
        printf("**********************************************\n");
        printf("\t1. Tea - 10/-\n");
        printf("\t2. Coffee / Milk / Boost / Lemon Tea / Water Bottle - 20/-\n");
        printf("\t3. Idly / Bonda / Plain dosa / Upma / Poha - 30/-\n");
        printf("\t4. Sambar idly / Wada / Onion / Masala dosa / Poori - 40/-\n");
        printf("\t5. Sambar wada / Veg Biryani / Paneer dosa - 50/-\n");
        printf("\t6. Bill\n");
        printf("\t7. Cancel\n");
        printf("\t8. Close\n");
        printf("**********************************************\n");        printf("\tEnter your option: ");
        scanf("%d", &op);        if (op >= 1 && op <= 5) {
            printf("Enter Quantity: ");
            scanf("%d", &qty);
        }        switch (op) {
            case 1: amt += qty * 10; break;
            case 2: amt += qty * 20; break;
            case 3: amt += qty * 30; break;
            case 4: amt += qty * 40; break;
            case 5: amt += qty * 50; break;            case 6: 
                printf("\nYour total billed amount = Rs. %d\n", amt);
                amt = 0; // reset after billing
                break;            case 7:
                printf("\nYour order is cancelled.\n");
                amt = 0;
                break;            case 8:
                printf("\nApplication Terminated. Thank you!\n");
                exit(0);            default:
                printf("\nInvalid Option! Try again.\n");
        }
    }    return 0;
}

🔹 Sample Run

************ HOTEL SAI BALAJI ************
1. Tea - 10/-
2. Coffee ... - 20/-
3. Idly ... - 30/-
...
Enter your option: 1
Enter Quantity: 2

Enter your option: 3
Enter Quantity: 1Enter your option: 6
Your total billed amount = Rs. 50