lvalues and rvalues

Variable names are said to be lvalues (for “left values”) because they can be used on the left side of an assignment operator. Constants are said to be rvalues (for “right values”) because they can be used on only the right side of an assignment operator. Lvalues can also be used as rvalues, but not vice versa.

There’s another equally unpleasant situation. Suppose you want to assign a value to a variable with a simple statement like

but instead write

Here, too, this is not a syntax error. Rather, the compiler simply evaluates the conditional expression. If x is equal to 1, the condition is true and the expression evaluates to the value true. If x is not equal to 1, the condition is false and the expression evaluates to the value false. Regardless of the expression’s value, there’s no assignment operator, so the value simply is lost. The value of x remains unaltered, probably causing an execution-time logic error. Unfortunately, we do not have a handy trick to help you with this problem!