Logical AND OR and NOT

Logical AND

In simple terms, && is true (1) if both sides of the expression returns NOT 0.

For Example: 

	/* These all return TRUE (1) */

	if (4 && 5) return();

	i=3;
	j=2;
	return( i && j);
The expression is evaluated 'Left to Right' If any part of the expression returns ZERO - The evaluation ends.

THIS CAN CAUSE SERIOUS PROBLEMS.

For example: 

	k=0;
	i=3;
	j=2;
	if ( i-i && j++) k=1
The left side (i-i) resolves to 0, so j is not incremented and k is not changed.

Logical OR

OR also evaluates 'Left to Right' and will stop when an expression returns true.

SO WATCH YOUR BACK.... 

	k=0;
	i=3;
	j=2;
	if ( i+i && j++) k=1
What are j and k going to be when this code is executed?????

Logical NOT

NOT reverses the logical state of its operand. If the operand is 0, 1 is returned, else 0 is returned. 
	!4	/* Returns 0	*/
	!-4	/* Returns 0	*/
	!1	/* Returns 0	*/
	!0	/* Returns 1	*/

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Martin Leslie

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