C++ Lessons : 12.1. Boolean Expressions

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Boolean Expression

A Boolean expression returns a boolean value that is either 1 (true) or 0 (false).

This is useful to build logic, and find answers.

You can use a comparison operator, such as the greater than (>) operator, to find out if an expression (or variable) is true or false:

Example

int x = 10;
int y = 9;
cout << (x > y); // returns 1 (true), because 10 is higher than 9

Or even easier:

Example

cout << (10 > 9); // returns 1 (true), because 10 is higher than 9

In the examples below, we use the equal to (==) operator to evaluate an expression:

Example

int x = 10;
cout << (x == 10);  // returns 1 (true), because the value of x is equal to 10

Example

cout << (10 == 15);  // returns 0 (false), because 10 is not equal to 15

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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;

cout << (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) {
  cout << "Old enough to vote!";
} else {
  cout << "Not old enough to vote.";
}

// Outputs: Old enough to vote!

Booleans are the basis for all C++ comparisons and conditions.

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