The bool Type and Boolean Expressions

Boolean Data Type — bool

In C++, data type bool is used to represent Boolean data. Each bool constant or variable contains one of two values:true or false.

true and false are two C++ constants.
true has the value 1.
false has the value 0.

If a testing expression is not of bool type,
it is coerced to bool type automaticaly when it is evaluated.
A nonzero value is coerced to true and a zero value is coerced to false.

Boolean Expressions

A Boolean expression can be a simple Boolean value, or it can be a more complex expression involving one or more relational and logical operators. Relational operators take two operands and test the relationship between them. The following table shows the relational operators and the corresponding C++ symbols.

Relational Operators
C++ Symbol	Description
==	equal to
!=	not equal to
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to

For example, The Boolean expression

	number1 < number2

is evaluated to true if the value stored in number1 is less than the value stored in number2, and evaluated to false otherwise.

When a relational operator is applied between variables of type char, the assertion is in terms of where the two operands fall in the collating sequence of a particular character set. For example,

	character1 < character2

is evaluated to true if the value stored in character1 comes before the character stored in character2 in the collating sequence of the machine on which the expression is being evaluated. You can think of collating sequence as being in alphabetic order to help you understand it. The ASCII character set is widely used as a collating sequence.

A simple Boolean expression is either a Boolean variable or a Boolean constant or an expression involving the relational operators that evaluates to either true or false. These simple Boolean expressions can be combined using logical operations defined on Boolean values. There are three Boolean operators: AND, OR and NOT. Here is a table showing how they are used in C++.

Logical Operators
C++ Symbol	Description
&&	The and Boolean operator: And is a binary operator - placed between two boolean expressions. If an operand is not already a boolean expression, it will be coerced to true or false. If both operands are true, the result is true. Otherwise, the result is false.
\|\|	The or Boolean operator: Or is a binary operator - placed between two boolean expressions. If an operand is not already a boolean expression, it will be coerced to true or false. If one or both operands are true, the result is true. Otherwise, if both operants are false, the result is false.
!	The not Boolean operator. Not reverses the value of its operand It is a unary operator placed before its operand. If the operand is not already a boolean expresssion, it will be coerced to true or false. If the operand is true, the result is false. If the operand is false, the result is true.

Precedence of Operators

If relational operators and Boolean operators are combined in the same expression in C++, the Boolean operator NOT ! has the highest precedence, the relational operators have the next highest precedence, and the Boolean operators AND && and OR || have the lowest. Expressions in parentheses are always evaluated first.

The following table summarizes the precedence of all the C++ operators we have seen so far.

				Highest Precedence
					|
	(  )				|
					|
	++x  --x			|
					|
	!  Unary +   Unary -		|
					|
	*  /  %				|
					|
	+  -				|
					|
	<<   >>				|
					|
	<  <=  >   >=			|
					|
	==  !=				|
					|
	&&				|
					|
	||				|
					|
	=				|
					|
	x++  x--			|
					V
				Lowest Precedence

Operators in the same line in the table have the same precedence. If an expression contains several operators with the same precedence, most of the operators group from left to right. Some operators have different precedence based on where variables are in relation to them, for these an x represents the variable.