Branch and loop statements in C language learning

Branch and loop statements

Branch statement

Branch statements are also called conditional judgment statements

• if
• switch

if The grammatical structure of a sentence

1. if ( expression )
   sentence ;
2. if( expression )
   sentence 1;
   else
   sentence 2;
3. if ( expression 1)
   sentence 1;
   if else ( expression 2)
   sentence 2;
   else
   sentence 3;
   If the expression is true, the statement executes
   C In language 0 Said the false , Not 0 Said really
   And that is else With the nearest one if Match

   switch The grammatical structure of a sentence

             switch It is often used to deal with multi branch situations 
   

   switch( Integer expression )
   {
   case Integral constant expression ：
   sentence ;
   }

• stay switch Statement break
  Such as ：

#include <stdio.h>
int main()
{
    
    int day = 6;
    switch (day)
    {
    
    case 1:
            printf(" Monday \n");
            break;
        case 2:
            printf(" Tuesday \n");
            break;
        case 3:
            printf(" Wednesday \n");
            break;
        case 4:
            printf(" Thursday \n");
            break;
        case 5:
            printf(" Friday \n");
            break;
        case 6:
            printf(" Saturday \n");
            break;
        case 7:
            printf(" Sunday \n");
            break;
    }
    return 0;
}

stay switch Collocation in sentences break Implement branch
break sentence The practical effect is to divide the statement list into different branches .

default Clause

default：
It can be written in any case The front and back of the car .
When switch The value of the expression does not match all case The value of the tag , This default The statement following the clause will execute .

Every switch Only one... Can appear in the statement default Clause .

Loop statement

• while
• for
• do while

while loop

while( expression )
Loop statement ;
for example ：
Print... On the screen 1~10 The number of .

#include <stdio.h>
int main()
{
    
 int i = 1;
 while(i<=10)
 {
    
 printf("%d ", i);
 i = i+1;
 }
 return 0;
}

It's basically like this .

for loop

for( expression 1; expression 2; expression 3)
Loop statement ;
expression 1
expression 1 For the initialization part , Used to initialize loop variables .
expression 2
expression 2 For the conditional judgment part , Used to determine when a loop ends .
expression 3
expression 3 For the adjustment part , For adjustment of cyclic conditions .
for example ：
Use for loop Print... On the screen 1-10 The number of .

#include <stdio.h>
int main()
{
    
 int i = 0;
 //for(i=1/* initialization */; i<=10/* Judgment part */; i++/* Adjustment part */)
 for(i=1; i<=10; i++)
 {
    
 printf("%d ", i);
 }
 return 0;
}

do while loop

do Sentence syntax ：
do
Loop statement ;
while( expression );
for example ：
Use do while Loop printing 1~10 The number of .

#include <stdio.h>
int main()
{
    
 int i = 10;
 do
 {
    
 printf("%d\n", i);
 }while(i<10);
 return 0;
}

do while The characteristic of the statement is that the loop executes at least once , First execute the statement once, and then judge whether the expression is true

In a loop statement break and continue

In the loop, whenever you encounter break, Terminate the cycle directly , The cycle is over , No more cycles .
continue Is used to terminate the cycle , In this cycle continue The following code is no longer executed , Instead, jump directly to the judgment part of the loop statement , Make the entry judgment of the next cycle .
for example ：
Use continue;

#include <stdio.h>
int main()
{
    
	int i = 0;
	while (i <= 10)
	{
    
		i = i + 1;
		if (i == 5)
			continue;
		printf("%d ", i);
		
	}
	return 0;

Its output is

Use break;

#include <stdio.h>
int main()
{
    
	int i = 0;
	while (i <= 10)
	{
    
		i = i + 1;
		if (i == 5)
			break;
		printf("%d ", i);
		
	}
	return 0;

come on. ！！！