Logical Operators Part 1

Part of the Fundamentals section of Coddy's C++ journey — lesson 23 of 74.

Logical operators are used to check combinations of comparisons that return true or false.

For example the following statement contains two comparisons:

Is 5 greater than 3 and less than 6?

Operator	Meaning	Example
`&&`	And - `true` if all operands are `true`	`a && b`
`\|\|`	Or - `true` if any operand is `true`	`a \|\| b`
`!`	Not - `true` if the operand is `false`	`!a`

Let's see some examples:

5 is greater than 3 and 1 equals 1:

bool b1 = (5 > 3) && (1 == 1); // holds true

Explanation: All of the operands are true, so b1 will hold true (and operation is true if both operands are true) .

5 is not equals 4 or 5 equals 2:

bool b2 = !(5 == 4) || (5 == 2); // holds true

Explanation: The first operand (5 != 4) is true so b2 is also true (or operation is true if either one of the operands is true)

1 is not equals 1 or false:

bool b3 = !(1 == 1) || false; // holds false

Explanation: All of the operands are false, so b3 will hold false (or operation).

3 is not greater than 4:

bool b4 = !(3 > 4); // holds true

Explanation: The operand is false, so b4 will hold true (not operation).

5 is not greater than 10 or 5 is not greater than 1:

bool b5 = !(5 > 10 || 5 > 1); // holds false

Explanation: 5 > 10 || 5 > 1 is true (one of the operands is true), so in total b5 is false (not operation).

Challenge

Beginner

You are given code. Replace the question marks of the variables bool b1 and bool b2 so that bool b3 holds true.

Take a moment to analyze the condition and think about what values would make it true.

There are many right solutions!

Cheat sheet

Logical operators are used to check combinations of comparisons that return true or false.

Operator	Meaning	Example
`&&`	And - `true` if all operands are `true`	`a && b`
`\|\|`	Or - `true` if any operand is `true`	`a \|\| b`
`!`	Not - `true` if the operand is `false`	`!a`

Examples:

bool b1 = (5 > 3) && (1 == 1); // true - both operands are true

bool b2 = !(5 == 4) || (5 == 2); // true - first operand is true

bool b3 = !(1 == 1) || false; // false - both operands are false

bool b4 = !(3 > 4); // true - negates false to true

bool b5 = !(5 > 10 || 5 > 1); // false - negates true to false

Try it yourself

#include <iostream>

int main() {
    // Type your code below
    bool b1 = ?;
    bool b2 = ?;
    bool b3 = b1 || b2;
    
    // Don't change the line below
    std::cout << "b3 = " << b3;
    return 0;
}