C — If Else

Basic if statement

Execute code only when a condition is true:

#include <stdio.h>

int main() {
    int temperature = 28;

    if (temperature > 25) {
        printf("It's warm outside!\n");
    }

    return 0;
}

if-else

Provide an alternative path:

#include <stdio.h>

int main() {
    int hour = 14;

    if (hour < 12) {
        printf("Good morning!\n");
    } else {
        printf("Good afternoon!\n");
    }

    return 0;
}

if-else if-else

Check multiple conditions:

#include <stdio.h>

int main() {
    int score = 85;

    if (score >= 90) {
        printf("Grade: A\n");
    } else if (score >= 80) {
        printf("Grade: B\n");
    } else if (score >= 70) {
        printf("Grade: C\n");
    } else if (score >= 60) {
        printf("Grade: D\n");
    } else {
        printf("Grade: F\n");
    }

    return 0;
}

Important: Evaluate conditions from most specific to least specific. Once a condition matches, subsequent conditions are skipped.

Nested if

An if inside another if:

#include <stdio.h>

int main() {
    int age = 25;
    int hasID = 1;

    if (age >= 18) {
        if (hasID) {
            printf("Entry granted.\n");
        } else {
            printf("Please show your ID.\n");
        }
    } else {
        printf("Sorry, you must be 18+.\n");
    }

    return 0;
}

Switch statement

Match a value against multiple cases:

#include <stdio.h>

int main() {
    int day = 3;

    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:
        case 7:
            printf("Weekend!\n");
            break;
        default:
            printf("Invalid day\n");
            break;
    }

    return 0;
}

Always use break after each case. Without it, execution "falls through" to the next case:

#include <stdio.h>

int main() {
    int month = 8;
    int days;

    switch (month) {
        case 2:
            days = 28; // Assume non-leap year
            break;
        case 4: case 6: case 9: case 11:
            days = 30;
            break;
        default:
            days = 31;
            break;
    }

    printf("Month %d has %d days\n", month, days);
    return 0;
}

Switch limitations

Switch only works with integer-compatible types:

#include <stdio.h>

int main() {
    // Valid switch types
    int i = 5;
    char c = 'A';
    enum Color { RED, GREEN, BLUE } color = GREEN;

    switch (i) { /* OK */ }
    switch (c) { /* OK — char promotes to int */ }
    switch (color) { /* OK — enum promotes to int */ }

    // Invalid switch types
    // float f = 3.14;
    // switch (f) { } // Error: float not allowed

    // const char *s = "hello";
    // switch (s) { } // Error: pointer not allowed

    return 0;
}

Ternary operator

Compact if-else for simple expressions:

#include <stdio.h>

int main() {
    int age = 20;
    const char *label = (age >= 18) ? "Adult" : "Minor";
    printf("Label: %s\n", label);

    int a = 5, b = 10;
    int max = (a > b) ? a : b;
    printf("Max: %d\n", max);

    return 0;
}

Combining conditions

Use logical operators for compound conditions:

#include <stdio.h>

int main() {
    int age = 25;
    int income = 50000;

    // AND: both must be true
    if (age >= 18 && income >= 30000) {
        printf("Qualifies for premium card.\n");
    }

    // OR: at least one must be true
    if (age < 12 || age > 65) {
        printf("Discounted ticket.\n");
    }

    // NOT: inverts the condition
    int isBanned = 0;
    if (!isBanned) {
        printf("Access granted.\n");
    }

    return 0;
}

Best practices

#include <stdio.h>

// GOOD: Early returns reduce nesting
const char *getDiscount(int age, int isMember) {
    if (age < 0) return "Invalid age";
    if (isMember) return "20% off";
    if (age < 12) return "50% off";
    if (age > 65) return "15% off";
    return "No discount";
}

int main() {
    printf("Discount: %s\n", getDiscount(25, 1));

    // GOOD: Use switch for multiple related conditions
    int code = 200;
    const char *message;
    switch (code) {
        case 200: message = "OK"; break;
        case 404: message = "Not Found"; break;
        case 500: message = "Server Error"; break;
        default:  message = "Unknown"; break;
    }
    printf("%d: %s\n", code, message);

    return 0;
}

Mini Practice

Write C code that:

1. Uses if-else to check if a number is positive, negative, or zero
2. Uses switch to map a grade (A-F) to a description
3. Combines conditions with && and ||
4. Uses the ternary operator for a simple conditional

Up Next

In the next lesson, you'll learn about Loops — for, while, and do-while in C.