If & Else

Life is full of decisions — and so is code. You'll constantly need your program to pick a path based on conditions. That's where if, else if, and else come in.

The if Statement

The simplest form: if something is true, do this thing. If not, skip it.

#include <stdio.h>
int main() {
  int age = 18;
  if (age >= 18) {
    printf("You can vote!\n");
  }
  return 0;
}
    

Adding else if and else

When you need more than two branches, chain them with else if. The first matching condition wins, and the rest are skipped.

#include <stdio.h>
int main() {
  int score = 85;
  if (score >= 90) {
    printf("Grade A\n");
  } else if (score >= 75) {
    printf("Grade B\n");
  } else if (score >= 50) {
    printf("Grade C\n");
  } else {
    printf("Grade F\n");
  }
  return 0;
}
    

Nested if Statements

You can put an if inside another if. Handy when you need to check a second condition only after the first one passes.

#include <stdio.h>
int main() {
  int x = 10, y = 5;
  if (x > 0) {
    if (y > 0) {
      printf("Both are positive\n");
    }
  }
  return 0;
}
    

Truthy and Falsy in C

C doesn't have a boolean type by default. Instead, zero is false and anything non-zero is true. So if (1) always runs, and if (0) never does.

#include <stdio.h>
int main() {
  if (1) {
    printf("This always prints\n");
  }
  if (0) {
    printf("This never prints\n");
  }
  if (-1) {
    printf("Negative numbers are also true!\n");
  }
  return 0;
}