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Examples using logical operators

(i < 10)  &&  (j > 0)
((x + y) <= 15) || (i == 5)
!((i >= 10) || (j <= 0))
(i < 10) && 0

Note that in the last example an actual truth value ( 0 - false) was used as one of the operands of &&, this means that whatever the value of i this logical expression evaluates to false (Why?). In these examples brackets have been used to make the order of application of operators clear. However, in the main, they are not strictly necessary if the precedence rules already considered for arithmetic operators are extended to include relational and logical operators. The consequent extended Operator Precedence Table for C++ is:

     highest - evaluate first

     ()             brackets
     !  +  -        logical not, unary plus, unary minus
     *  /  %        multiply, divide, modulus
     +  -           add, subtract
     < <= > >=      less than, less than or equal,
                    greater than, greater than or equal
     == !=          equal, not equal
     &&             logical and
     ||             logical or
     =              assignment

     lowest - evaluate last

Be careful not to confuse the assignment operator = with the logical equality operator ==.

Using this table with the following expression

x + y < 10 && x/y == 3 || z != 10

shows that the operators are evaluated in the order /, +, <, ==, !=, && and ||. This is equivalent to bracketting the expression as follows:

((((x + y) < 10) && ((x/y) == 3)) || (z != 10))

Similarly the expressions written in bracketted form above could be written without brackets as:

i < 10  &&  j > 0
x + y <= 15 || i == 5
!(i >= 10 || j <= 0)
i < 10 && 0

Now that logical expressions (or conditions) in C++ have been covered it is possible to move on and look at the conditional control structures in C++.