If-Else & Decision Making in C

The if statement in C lets your program make decisions: it runs a block of code only when a condition is true. Add else to handle the false case, and chain else if to test several conditions in order. This is how a program chooses one path over another.

The basic if

if (condition) {
    /* runs only when condition is non-zero (true) */
}

In C, any non-zero value is "true" and zero is "false". So if (5) always runs, and if (0) never does.

#include <stdio.h>

int main(void) {
    int marks = 72;

    if (marks >= 40) {
        printf("Pass\n");   /* runs because 72 >= 40 is true */
    }
    return 0;
}

Adding else

else gives the alternative when the condition is false:

int age = 15;

if (age >= 18) {
    printf("Adult\n");
} else {
    printf("Minor\n");   /* this runs */
}

The else-if ladder

To check several mutually exclusive conditions, chain them. C tests each in order and stops at the first match:

#include <stdio.h>

int main(void) {
    int score = 85;

    if (score >= 90) {
        printf("Grade A\n");
    } else if (score >= 75) {
        printf("Grade B\n");   /* first true branch -> runs, rest skipped */
    } else if (score >= 50) {
        printf("Grade C\n");
    } else {
        printf("Fail\n");
    }
    return 0;
}

Once a branch matches, the remaining else if and else blocks are skipped entirely.

Nested if

You can put an if inside another if when one decision depends on another:

int loggedIn = 1;
int isAdmin = 0;

if (loggedIn) {
    if (isAdmin) {
        printf("Admin panel\n");
    } else {
        printf("User dashboard\n");
    }
}

Keep nesting shallow — deep nesting is hard to read. Often logical operators like && let you flatten it.

The ternary shortcut

For a simple either/or assignment, the ternary operator ?: is compact:

int a = 7, b = 3;
int max = (a > b) ? a : b;   /* if a>b pick a, else pick b -> 7 */
printf("Max: %d\n", max);

Read it as: condition ? value-if-true : value-if-false. Use it only for short, simple choices; for anything with multiple statements, a full if-else is clearer.

How C decides true and false

There is one idea worth fixing firmly: in C there is no separate boolean type in the classic sense — zero is false, and any non-zero value is true. That is why if (count) runs whenever count is not zero, and if (!ptr) runs when a pointer is NULL (zero). Comparisons like a > b produce exactly 1 for true and 0 for false. Knowing this lets you write concise, idiomatic conditions — but it is also why the = versus == mistake is so dangerous: an assignment evaluates to the value assigned, which C then tests for truthiness.

Common mistakes

• = instead of ==: if (x = 5) assigns 5 and is always true. Use == to compare.
• Stray semicolon: if (x > 0); ends the statement immediately, so the block below always runs. Don't put ; right after the condition.
• Missing braces with multiple statements: without { }, only the first line belongs to the if. Always use braces.
• Comparing floats with ==: rounding makes this unreliable; compare a difference against a small tolerance instead.
• Forgetting else if is ordered: put the most specific or highest condition first, or a broad earlier branch will swallow the cases you wanted later.

FAQ

Do I always need else? No. Use if alone when there's nothing to do in the false case.

Is if-else or switch better? For many comparisons of one variable against constant values, a switch-case is often cleaner. For ranges and complex conditions, use if-else.

Continue at the hub C Programming, or read Operators in C and Switch-Case in C.

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