Suspended else problem

In the air else problem

Let's look at a very simple piece of code , Try to find out the running result of the program ：

#include<stdio.h>
int main()
{
    
	int a = 0;
	int b = 2;
	if (a == 1)
		if (b == 2)
			printf("hehe\n");
	else
		printf("haha\n");
	return 0;
}

If your answer is ：haha, Congratulations on your wrong answer ！ Don't be discouraged , Think again …; Now? , If you have thought it over, the answer is ：hehe, Then I'm sure you're definitely guessing . What will be the output of this program ？

The answer is unexpected , This code does not output anything . Then why ？ This is a little bit of knowledge I want to share today that you will make mistakes if you are not careful ：“ In the air else problem ”. First , Did you learn C The old fellow of the language should know ,if An expression can only be followed by a clause , If the sentence contains more than one sentence , Must be enclosed in curly braces to become a Sentence block （ Because a statement block can be treated as a statement ）.

if (a == 1)
	  if (b == 2)
			printf("hehe\n");

Then I want to ask ： Uppermost if（a==1） Who is the sentence after the expression ？ Be careful here ,if（a==1） The clause of the expression is not if（b==2） This expression , It is ：

if (b == 2)
	   printf("hehe\n");

because if The statement is actually a whole , therefore if The expression and the following sentence add up to a complete statement , If only if expression , That is not recognized by grammar . Now that I've thought of it , Let me ask again ,if-else Can a statement be treated as a statement ？ The answer, of course, is ： Sure . Now if you look back at the previous code, you will suddenly see the light , I see how it feels ！！！

#include<stdio.h>
int main()
{
    
	int a = 0;
	int b = 2;
	if (a == 1)
		if (b == 2)
			printf("hehe\n");
	else
		printf("haha\n");
	return 0;
}

Is that so? , So simple , But why are you still wrong . There is such a mistake , The root cause is the bad code style , You read this code according to your code style , So I habitually think this else It's the one aligned with it if Matched , Thus leading to tragedy . I would like to mention one more point here , It's about else The matching of ： No matter what you do if—else How to nest , Alignment misalignment , Do you like it , I else Only with the nearest if To match . So how to avoid this problem ？ Then we must develop a good code style . as follows ：

#include<stdio.h>
int main()
{
    
	int a = 0;
	int b = 2;
	if (a == 1)
	{
    
		if (b == 2)
		{
    
			printf("hehe\n");
		}
		else
		{
    
			printf("haha\n");
		}
	}
	return 0;
}

It's clear at a glance ！！！

If this blog is helpful to you , Give bloggers a free like to show encouragement. Welcome to like comment collection ️, thank you ！！！
If you have any questions or different opinions , Welcome to the comment area .