5-2. Logical expression and short-circuit problem

1. And: && (about two expressions are true only for true)

2. Or: || (about at least one of the two expressions is true only for true)

3. non:! (Equivalent to negate, to really make false non-operational, non-operational for false do is true)

4. int m = 20;
     	int n = 30;
     
     	if (m == 20 && n == 30)
     	{
     		cout << "m == 10 , n == 30" << endl;
     	}
     	if (m == 20 || n == 40)
     	{
     		cout << "两个表达式至少一个为真" << endl;
     	}
     	if (!(m < 20))
     	{
     		cout << "!(m < 20)" << endl;
     	}
     	/*结果：
     
     	m == 10 , n == 30
     	两个表达式至少一个为真
     	!(m < 20)
     	*/
   

5. Short-circuit problem

• Mainly for logic and logical or
• For a logical and &&: if the first expression is detected is false, then the rest of the expression will not be checked.
• For a logical or ||: if the detected first expression is true, then the rest of the expression does not check.

6. By short-circuiting problem to determine whether the function of a class is initialized, it is empty

   MyClass *myClass;
   ...
   //myClass.process()
   if(myClass != NULL && myClass.process())
   {
       ...
   }