C if-else Statement

if-else is a fork in the road: if the condition is true you go one way, and otherwise you go the other. One of the two always runs.

In this page:

What is if-else?
Pass or Fail Check
Even or Odd Divider
Voting Eligibility
Nested if-else

Syntax

if (condition) {
  // runs when condition is true
} else {
  // runs when condition is false
}

What is if-else?

if-else covers exactly two possible outcomes for a condition: the if block runs when the condition is true, and the else block runs instead whenever it's false, so exactly one of the two paths always executes.

Example: What is if-else?

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	// Declare age and set it to 15
	int age = 15;
	// Check whether age >= 18
	if (age >= 18) {
		// Print formatted text to the screen
		printf("Adult");
	} else {
		// Print formatted text to the screen
		printf("Minor");
	}
	// Return 0 to signal that the program finished successfully
	return 0;
}

Pass or Fail Check

Comparing a score against a passing threshold with if-else -- if (score >= 50) ... else ... -- cleanly separates the pass and fail outcomes into two distinct, mutually exclusive code paths.

Example: Pass or Fail Check

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	// Declare score and set it to 40
	int score = 40;
	// Check whether score >= 50
	if (score >= 50) {
		// Print formatted text to the screen
		printf("Pass");
	} else {
		// Print formatted text to the screen
		printf("Fail");
	}
	// Return 0 to signal that the program finished successfully
	return 0;
}

Even or Odd Divider

Testing n % 2 == 0 inside an if-else lets a single conditional handle both the even and odd cases in one block, rather than needing two separate if statements to cover both outcomes.

Example: Even or Odd Divider

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	// Declare n and set it to 7
	int n = 7;
	// Check whether n % 2 == 0
	if (n % 2 == 0) {
		// Print formatted text to the screen
		printf("Even");
	} else {
		// Print formatted text to the screen
		printf("Odd");
	}
	// Return 0 to signal that the program finished successfully
	return 0;
}

Voting Eligibility

if-else is a natural fit for eligibility checks, such as verifying if (age >= 18) ... else ... to separate users who qualify for something from those who don't, in a single readable comparison.

Example: Voting Eligibility

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	// Declare age and set it to 16
	int age = 16;
	// Check whether age >= 18
	if (age >= 18) {
		// Print formatted text to the screen
		printf("Can vote");
	} else {
		// Print formatted text to the screen
		printf("Cannot vote");
	}
	// Return 0 to signal that the program finished successfully
	return 0;
}

Nested if-else

Nesting an if-else inside either branch of an outer if-else lets you handle sub-decisions -- for example, once you know a number is positive, a nested if-else can further classify it as even or odd.

Example: Nested if-else

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	// Declare n and set it to 8
	int n = 8;
	// Check whether n > 0
	if (n > 0) {
		// Check whether n % 2 == 0
		if (n % 2 == 0) {
			// Print formatted text to the screen
			printf("Positive even");
		} else {
			// Print formatted text to the screen
			printf("Positive odd");
		}
	} else {
		printf("Not positive");
	}
	// Return 0 to signal that the program finished successfully
	return 0;
}

Chapter Quiz — Complete all 11 topics to unlock

0/11 topics done

Complete these topics first:

← Previous Lesson C if Statement Next Lesson → C else-if Ladder