C Booleans

Booleans

Very often, in programming, you will need a data type that can only have one of two values, like:

  • YES / NO
  • ON / OFF
  • TRUE / FALSE

For this, C has a bool data type, which is known as booleans.

Booleans represent values that are either true or false.

Boolean Variables

In C, the bool type is not a built-in data type, like int or char.

It was introduced in C99, and you must import the following header file to use it:

#include <stdbool.h>

A boolean variable is declared with the bool keyword and can take the values true or false:

bool isProgrammingFun = true;
bool isFishTasty = false;

Before trying to print the boolean variables, you should know that boolean values are returned as integers:

  • 1 (or any other number that is not 0) represents true
  • 0 represents false

Therefore, you must use the %d format specifier to print a boolean value:

Example

// Create boolean variables
bool isProgrammingFun = true;
bool isFishTasty = false;

// Return boolean values
printf("%d", isProgrammingFun);   // Returns 1 (true)
printf("%d", isFishTasty);        // Returns 0 (false)

However, it is more common to return a boolean value by comparing values and variables.

Comparing Values and Variables

Comparing values are useful in programming, because it helps us to find answers and make decisions.

For example, you can use a comparison operator, such as the greater than (>) operator, to compare two values:

Example

printf("%d", 10 > 9);  // Returns 1 (true) because 10 is greater than 9

From the example above, you can see that the return value is a boolean value (1).

You can also compare two variables:

Example

int x = 10;
int y = 9;
printf("%d", x > y);

In the example below, we use the equal to (==) operator to compare different values:

Example

printf("%d", 10 == 10); // Returns 1 (true), because 10 is equal to 10
printf("%d", 10 == 15); // Returns 0 (false), because 10 is not equal to 15
printf("%d", 5 == 55);  // Returns 0 (false) because 5 is not equal to 55

You are not limited to only compare numbers. You can also compare boolean variables, or even special structures, like arrays (which you will learn more about in a later chapter):

Example

bool isHamburgerTasty = true;
bool isPizzaTasty = true;

// Find out if both hamburger and pizza is tasty
printf("%d", isHamburgerTasty == isPizzaTasty);

Remember to include the <stdbool.h> header file when working with bool variables.

Real Life Example

Let's think of a "real life example" where we need to find out if a person is old enough to vote.

In the example below, we use the >= comparison operator to find out if the age (25) is greater than OR equal to the voting age limit, which is set to 18:

Example

int myAge = 25;
int votingAge = 18;

printf("%d", myAge >= votingAge); // Returns 1 (true), meaning 25 year olds are allowed to vote!

Cool, right? An even better approach (since we are on a roll now), would be to wrap the code above in an if...else statement, so we can perform different actions depending on the result:

Example

Output "Old enough to vote!" if myAge is greater than or equal to 18. Otherwise output "Not old enough to vote.":

int myAge = 25;
int votingAge = 18;

if (myAge >= votingAge) {
  printf("Old enough to vote!");
} else {
  printf("Not old enough to vote.");
}

Booleans are the basis for all comparisons and conditions.

You will learn more about conditions (if...else) in the next chapter.