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Making Decisions (if / else)

Your program does not always have to do the same thing every time. An if statement lets you run a block of code only when a condition is true.

if

if (condition) {
    // code that runs when condition is true
}

The condition is an expression that evaluates to true or false. If it is true, the code inside the { } runs. If it is false, that block is skipped entirely.

Example

int score = 85;

if (score >= 90) {
    printf("Grade: A\n");
}

Because 85 >= 90 is false, nothing is printed.

else

else provides a block that runs when the if condition is false:

int score = 85;

if (score >= 90) {
    printf("Grade: A\n");
}
else {
    printf("Grade: below A\n");
}

Exactly one of the two blocks will run, never both.

else if — more than two cases

Chain multiple conditions with else if:

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 {
    printf("Grade: below C\n");
}

The conditions are checked top to bottom. The first one that is true runs its block, and the rest are skipped. With score = 85, the second condition (>= 80) matches and Grade: B is printed.

Comparison operators

Operator Meaning
== equal to
!= not equal to
< less than
> greater than
<= less than or equal to
>= greater than or equal to

= vs ==

A single = assigns a value. A double == compares two values. Writing if (x = 5) instead of if (x == 5) is a classic C mistake — it assigns 5 to x instead of comparing.

See also