C Control Flow

if Statement

The if statement executes a block of code only if the condition is true (non-zero in C).

if (condition) {
    // executes if condition is true
}

if-else Statement

if (condition) {
    // executes if condition is true
} else {
    // executes if condition is false
}

if-else-if Ladder

Used to test multiple conditions in sequence. The first true condition executes and the rest are skipped.

if (condition1) {
    // ...
} else if (condition2) {
    // ...
} else if (condition3) {
    // ...
} else {
    // default
}

switch-case

The switch statement tests a variable against a list of values (cases). Each case must end with break to prevent fall-through. The default case runs if no case matches.

if-else-if Ladder — Grade Calculator

#include <stdio.h>

int main() {
    int marks;
    printf("Enter marks (0-100): ");
    scanf("%d", &marks);

    if (marks >= 90) {
        printf("Grade: A+ (Excellent)\n");
    } else if (marks >= 80) {
        printf("Grade: A (Very Good)\n");
    } else if (marks >= 70) {
        printf("Grade: B (Good)\n");
    } else if (marks >= 60) {
        printf("Grade: C (Average)\n");
    } else if (marks >= 50) {
        printf("Grade: D (Pass)\n");
    } else {
        printf("Grade: F (Fail)\n");
    }

    return 0;
}

/*
Enter marks (0-100): 85
Grade: A (Very Good)
*/

switch-case — Day of Week

#include <stdio.h>

int main() {
    int day;
    printf("Enter day number (1-7): ");
    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 number!\n");
    }

    // Fall-through example: weekend check
    switch (day) {
        case 6:
        case 7:
            printf("It's the weekend!\n");
            break;
        default:
            printf("It's a weekday.\n");
    }

    return 0;
}

Nested if — Largest of Three Numbers

#include <stdio.h>

int main() {
    int a, b, c;
    printf("Enter three numbers: ");
    scanf("%d %d %d", &a, &b, &c);

    if (a >= b) {
        if (a >= c) {
            printf("Largest: %d\n", a);
        } else {
            printf("Largest: %d\n", c);
        }
    } else {
        if (b >= c) {
            printf("Largest: %d\n", b);
        } else {
            printf("Largest: %d\n", c);
        }
    }

    return 0;
}

/*
Enter three numbers: 12 45 30
Largest: 45
*/

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C Control Flow

if Statement

if-else Statement

if-else-if Ladder

switch-case

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