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if, else if and else in C: Conditions, Nested if and the Ternary Operator

Learn conditional statements in C: if, if-else and else-if chains, conditions that are true when non-zero, combining conditions with && and ||, nested if and the dangling else, the ternary operator, and common mistakes such as = instead of ==.

Beginner7 min readUpdated
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The if statement runs code only when a condition is true. In C, "true" means any non-zero value, and "false" means zero.

if#

C
int temperature = 34;
if (temperature > 30) {
    printf("It's hot. Drink water!\n");
}
printf("Have a nice day.\n");
Output
It's hot. Drink water!
Have a nice day.

if-else#

C
int balance = 250, price = 400;
if (balance >= price) {
    printf("Payment successful\n");
} else {
    printf("You need %d more\n", price - balance);
}
Output
You need 150 more

else if chains#

Conditions are checked from top to bottom; only the first true branch runs:

C
#include <stdio.h>

char grade(int marks) {
    if (marks >= 90) {
        return 'A';
    } else if (marks >= 75) {
        return 'B';
    } else if (marks >= 50) {
        return 'C';
    } else {
        return 'F';
    }
}

int main(void) {
    printf("%c %c %c %c\n", grade(95), grade(80), grade(62), grade(30));
    return 0;
}
Output
A B C F

Order matters: with marks >= 50 first, 95 would get a C.

Combining conditions#

C
int age = 25, has_licence = 1, is_weekend = 0;
if (age >= 18 && has_licence) {
    printf("Can rent a car\n");
}
if (is_weekend || age < 12) {
    printf("Discount\n");
} else {
    printf("Full price\n");
}
Output
Can rent a car
Full price

Non-zero is true#

Any value can be used as a condition:

C
int items = 0;
if (items) {
    printf("Cart has items\n");
} else {
    printf("Cart is empty\n");
}
if (!items) {
    printf("Still empty\n");
}
Output
Cart is empty
Still empty

For pointers, if (ptr) means "the pointer is not NULL" (Pointers).

Nested if and the dangling else#

An else belongs to the nearest if that does not already have one, whatever the indentation suggests:

C
int x = 5, y = -1;
if (x > 0)
    if (y > 0)
        printf("both positive\n");
else
    printf("this else belongs to 'if (y > 0)'\n");
Output
this else belongs to 'if (y > 0)'

Always use braces to make the structure explicit; GCC warns about this case with -Wall.

The ternary operator#

condition ? a : b chooses between two values:

C
int n = 7;
printf("%d is %s\n", n, n % 2 == 0 ? "even" : "odd");
Output
7 is odd

Common mistakes#

Practice#

Practice exercise

Write a function int is_leap(int year) that returns 1 for leap years (divisible by 4, except centuries, unless divisible by 400) and test it with 2024, 1900, 2000 and 2026.

Show solution
C
#include <stdio.h>

int is_leap(int year) {
    if (year % 400 == 0) return 1;
    if (year % 100 == 0) return 0;
    return year % 4 == 0;
}

int main(void) {
    int years[] = {2024, 1900, 2000, 2026};
    for (int i = 0; i < 4; i++) {
        printf("%d: %s\n", years[i], is_leap(years[i]) ? "leap" : "not leap");
    }
    return 0;
}
Output
2024: leap
1900: not leap
2000: leap
2026: not leap

Key takeaway#

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