logical-and-operator-amp-amp.md

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Logical AND Operator: && | Microsoft Docs		11/04/2016			cpp-language		language-reference	&&	C++	logical AND operator AND operator && operator	50cfa664-a8c4-4b31-9bab-2f80d7cd2d1f	8	mikeblome	mblome	ghogen

Logical AND Operator: &&

Syntax

  
expression   
&&  
 expression  
  

Remarks

The logical AND operator (&&) returns the boolean value true if both operands are true and returns false otherwise. The operands are implicitly converted to type bool prior to evaluation, and the result is of type bool. Logical AND has left-to-right associativity.

The operands to the logical AND operator need not be of the same type, but they must be of integral or pointer type. The operands are commonly relational or equality expressions.

The first operand is completely evaluated and all side effects are completed before continuing evaluation of the logical AND expression.

The second operand is evaluated only if the first operand evaluates to true (nonzero). This evaluation eliminates needless evaluation of the second operand when the logical AND expression is false. You can use this short-circuit evaluation to prevent null-pointer dereferencing, as shown in the following example:

char *pch = 0;  
...  
(pch) && (*pch = 'a');  

If pch is null (0), the right side of the expression is never evaluated. Therefore, the assignment through a null pointer is impossible.

Operator Keyword for &&

The and operator is the text equivalent of &&. There are two ways to access the and operator in your programs: include the header file iso646.h, or compile with the /Za (Disable language extensions) compiler option.

Example

// expre_Logical_AND_Operator.cpp  
// compile with: /EHsc  
// Demonstrate logical AND  
#include <iostream>  
  
using namespace std;  
  
int main() {  
   int a = 5, b = 10, c = 15;  
   cout  << boolalpha  
         << "The true expression "  
         << "a < b && b < c yields "  
         << (a < b && b < c) << endl  
         << "The false expression "  
         << "a > b && b < c yields "  
         << (a > b && b < c) << endl;  
}  

See Also

C++ Built-in Operators Precedence and Associativity C++ Built-in Operators, Precedence and Associativity
C Logical Operators