Detailed explanation of C language branch statements

if else

1. if else Use
   such as “ When ：18<age<45” when , Output “ middle-aged person ”, Output in other cases “ error ”.

if(18<age&&45>age){
    
	printf(" middle-aged person ");
}else{
    
	printf(" error ");
}

Like this if else Use ,if Put conditions in brackets after , If the condition is true, output the following statement , Otherwise output else The sentence of .

Be careful “18<age<45” Writing in brackets is not direct “18<age<45”, Instead, separate them with logical statements , Otherwise, the result will be like this

No matter what number is output, the answer is middle-aged , Because I will judge first “18<age”, Then there are only two cases of this expression anyway , Only 1 and 0（ It's 1, Fake is 0）, And the result and 45 Compare the size , It's always 45 Big , The condition is always true , So always export middle-aged people .

2. if else Just follow the next sentence
   Not nested

if(0==a)
	printf("CSDN");
else
	printf("CS");

This is to output only the following statement , If there are many sentences, add {}, Make them a compound statement

if(0==a){
    
	printf("CSDN");
	a++;
	}
else{
    
	printf("CS");
	a++;
	}

nesting

if(0==a){
    
	printf("CSDN");
}	else if(1==a){
    
		printf("CSDN");
}else{
    
	printf("CS");
}

ad locum ,else if Count as a sentence , Because it only outputs two results .

3. else Always with the nearest if matching

int a = 0;
if(0==a)
	if(1==a)
	printf("CSDN");
	else
	printf("CS");
printf("CSGO");

Its result is “CSGO”, because else It's the nearest if Matching , That is to say 1==a the （ I deliberately put else Put it in the second if Below ）, So I suggest writing every time if else Use curly braces to enclose , In this way, mistakes can be avoided , Second, it can make the program look more beautiful .（ There will be a code style article in the future ）

switch

Talking about switch Before , Let's talk first. break and default.

break

break It means to break （ Permanent termination ） loop , It can also be understood as jumping out of this cycle .
We will talk about it in more detail later , More flexible .

default

default Means to go out , Non performance means . stay switch in , If except case Other than that Then output default Subsequent statements .
case Decide the entrance ,break Decide to export .（ This sentence is useful later ）

1. switch Use
   switch（ Integer expression ）{
   Statement item :
   }

Statement items are just some case sentence , such as ：

switch(day){
    
	case 1:
		printf(" Monday ");
	case 2:
		printf(" Tuesday ");
}

Simply put
case Integer expression :
sentence ;
Now take a complete example

This is a code to input the number and output the corresponding week , without break It would be like this
So I just answer the above words

case Decide the entrance ,break Decide to export .

But not everyone case You need to add break, such as （ This is to input the number to determine whether it corresponds to a working day or a rest day ）
This is to break Flexible use , Instead of blindly adding break.

Suggest ： At the end of the default It's better to add break The habit of , Because if you or other programmers want to default If you add other sentences after it , Then there may be repeated output .

2. switch The nested use of
   In fact, nested use is easy , Directly above
   There's no point , Hit at random , Take a look and you will know how to use nesting .