4.14. Logical operators

There are three logical operators in C++: AND, OR, and NOT, which are normally denoted by the symbols &&, || and !. The semantics (meaning) of these operators is similar to their meaning in English. For example x > 0 && x < 10 is true only if x is greater than zero AND less than 10.

even || n%3 == 0 is true if either of the conditions is true, that is, if the bool variable even is true OR the number is divisible by 3.

Finally, the NOT operator has the effect of negating or inverting a bool expression, so !even is true if even is false; that is, if the number is odd.

Logical operators often provide a way to simplify nested conditional statements.

Q1

Multiple Response: How could you re-write the following code using a single conditional?

if (x > 0) {
  if (x < 10) {
    cout << "x is a positive single digit" << '\n';
  }
}

if (x > 0 && x < 10) {...

This is exactly what the nested conditionals are saying.

if (x > 0 || x < 10) {...

|| represents "or", but we need both sides of the conditional to be true.

if (x > 0 ! x < 10) {...

The ! operator cannot be used to compare two sides of a conditional.

if ( !(x < 0) && !(x > 10) ) {...

If x = 0 or if x = 10, this expression will return true when it shouldn't.

if ( !(x <= 0) && !(x >= 10) ) {...

If it IS NOT what we don't want, then it IS what we want!

Check answer

Q2

Match the conditional statement to the correct boolean and the meaning of the operator in use, given n = 7.

!(n == 7) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

!(n >= 10) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

(n * 2 > 10 && n < 7) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

(n * 2 > 10 && n >= 7) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

(n%2 == 0 || n == 8) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

(n%2 == 1 || n == 8) Choose a definition false, "and" false, "not" false, "or" true, "and" true, "not" true, "or"

Check answer

Q3

Add a single logical operator to make the expression check if x is greater than or equal to 50

( x < 50 )

Check answer

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More to Explore

• logical operators from cppreference