7.5 Logical Operators

Logical operators are useful for combining two or more conditional statements into one. So far, this chapter has considered only individual conditional statements, such as (A > B), (A < D), (A == E), and so on. The following logical operators can be used to combine such statements: AND (&&), OR (||), and NOT (!). So, to determine whether variable X is within the range of 0 to 10, two conditional statements can be combined using logical operators as follows: (X >= 0) && (X <= 10). This whole expression will evaluate to true or false, depending on whether X falls within this range. The following list examines the logical operators more closely.

AND &&

Determines whether any conditional statements are true. This entire statement will only evaluate to true if all conditional statements are true; otherwise it will evaluate to false.
OR ||

Determines whether any one of a given set of conditional statements is true. If so, the statement will evaluate to true; otherwise it is false if all conditional statements are false.
NOT!

Determines whether the inverse of a condition is true.

Note

Logical operators in the context of AND were seen briefly in the section on chained inequalities in Chapter 2.

7.5.1 If Else Statements and Logical Operators

Since logical operators like AND and OR can be combined with conditional statements like (A > B), they can both affect If statements and If Else statements. Using logical operators with conditional statements means that several conditions can be specified in a single If statement. For example, if((a>b)&&(a<d)). The following code uses If Else statements with conditional and logical operators.

      #include <iostream>      int main()      {         int Number = 0;         std::cout<<"Enter a number\n";         std::cin >> Key;         if(Number < 10)         {            std::cout<<"Number less than 10\n";         }         if((Number >= 10) && (Number <= 30))         {            std::cout<<"Number from 10 to 30";         }         if(Number != 7)         {            std::cout<<"Number is not 7\n";         }         if((Number == 5) || (Number < 3))         {            std::cout<<"Number is equal to 5 or less than 3\n";         }         return 0;      }