C Return Values

A return value is the answer a function hands back when it finishes, like a vending machine giving you a snack. You can then use that answer in the rest of your program.

In this page:

The return Statement
Returning Integers
Returning Floating-Point Numbers
Returning Characters
Using Returned Values in Expressions

Syntax

return_type function_name(parameters) {
  return value;
}

void function_name() {
  return;  // optional, returns nothing
}

The return Statement

The return statement immediately ends a function's execution and, if the function has a non-void return type, sends a value back to whatever code called it -- any statements after return in that function never run.

Example: The return Statement

// Include standard input/output (printf, scanf)
#include <stdio.h>
int getFive() {
	// Send 5 back to the caller
	return 5;
	// Print formatted text to the screen
	printf("never runs");
}
// Program execution starts in main()
int main() {
	// Print formatted text to the screen
	printf("%d", getFive());
	// Return 0 to signal that the program finished successfully
	return 0;
}

Returning Integers

Declaring a function's return type as int means it hands back a whole number to its caller, which is the standard choice for functions computing counts, indexes, or results of integer arithmetic.

Example: Returning Integers

// Include standard input/output (printf, scanf)
#include <stdio.h>
int add(int a, int b) {
	// Send a + b back to the caller
	return a + b;
}
// Program execution starts in main()
int main() {
	// Print formatted text to the screen
	printf("%d", add(2, 3));
	// Return 0 to signal that the program finished successfully
	return 0;
}

Returning Floating-Point Numbers

When a calculation needs fractional precision, declaring the function's return type as float or double lets it hand back a decimal result instead of being forced to round to a whole number.

Example: Returning Floating-Point Numbers

// Include standard input/output (printf, scanf)
#include <stdio.h>
double divide(int a, int b) {
	// Send (double)a / b back to the caller
	return (double)a / b;
}
// Program execution starts in main()
int main() {
	// Print formatted text to the screen
	printf("%.2f", divide(7, 2));
	// Return 0 to signal that the program finished successfully
	return 0;
}

Returning Characters

A function can return char to hand back a single character result -- useful for functions that classify input or compute something like a grade letter based on a numeric score.

Example: Returning Characters

// Include standard input/output (printf, scanf)
#include <stdio.h>
char getGrade(int score) {
	// Send (score >= 90) ? 'A' : 'B' back to the caller
	return (score >= 90) ? 'A' : 'B';
}
// Program execution starts in main()
int main() {
	// Print formatted text to the screen
	printf("%c", getGrade(95));
	// Return 0 to signal that the program finished successfully
	return 0;
}

Using Returned Values in Expressions

A function's returned value can be used directly inside a larger expression -- like total = add(3, 4) * 2; -- without first storing it in an intermediate variable, since the call itself evaluates to that returned value.

Example: Using Returned Values in Expressions

// Include standard input/output (printf, scanf)
#include <stdio.h>
int add(int a, int b) {
	// Send a + b back to the caller
	return a + b;
}
// Program execution starts in main()
int main() {
	// Declare total and set it to add(3, 4) * 2
	int total = add(3, 4) * 2;
	// Print formatted text to the screen
	printf("%d", total);
	// Return 0 to signal that the program finished successfully
	return 0;
}

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