Foreword: Starting from this article, bloggers will continue to update several important basic grammar knowledge in C language from time to time.
Table of contents
2. Three major circulation bodies
2. Explanation of the cycle body
3. The two major keywords in the loop
1. What is a cycle
1. Definition of cycle
Loop, as the name suggests, is a loop, hahaha, just like that kind of spiral slide, circle by circle, layer by layer, the loop statement will be repeatedly executed under the constraints you set .
2. Three major circulation bodies
- while
- do while
- for
2. Explanation of the cycle body
1. while loop
The while loop is also called "while loop" , I only loop when you meet my restriction .
The grammatical structure of while:
while(expression)
{
loop statement;
}
The expression in () after while is the judgment condition , and only when the expression is true , it will enter the while loop and execute the loop statement.
Simple code display:
//打印1-10的数字
#include<stdio.h>
int main()
{
int i = 1;
while(i <= 10)
{
printf("%d ",i);
i++;
}
return 0;
}2.do while loop
Like the while loop, do while will only execute the loop if the expression is true .
The grammatical structure of do while:
do
{
loop statement;
}while(expression);
The only difference between a do while loop and a while loop is that a do while loop executes at least once , while a while loop may never execute at all .
As in the above code, the expression is obviously false , but 1 will still be printed out. This is the magic of the do while loop. Why? Because the codes are executed one by one from top to bottom , the judgment condition of do while is after the loop statement , so naturally the loop statement is executed first, and then the judgment is made .
3. for loop
The for loop can be described as the big brother of the three loops , and it is also the most versatile loop body.
Syntax structure of for loop:
for (initialization; judgment expression; adjustment statement)
{
loop body;
}
The for loop integrates initialization, judgment expressions, and adjustment statements , and only needs to enter the content you want to loop in the loop body. Its execution sequence is: initial--->judgment--->judgment passed--->execute loop body--->adjust statement--->judgment--->judgment not passed--->end loop .
#include<stdio.h>
int main()
{
int i = 1;
for (i = 1; i <= 10; i++)
{
printf("%d ", i);
}
return 0;
}Here we add some variant usage of for loop:
for( ; ; )
{
printf("hehe");
}
The initialization, judgment statement, and adjustment statement in the for loop can all be omitted . It should be noted that when the judgment statement is omitted , it will always be true by default , that is, print "hehe" in an endless loop.
int i = 0;
int j = 0;
for (; i < 3; i++)
{
for (; j < 3; j++)
{
printf("hehe\n");
}
}
Given such a nested loop code, how many "hehe" will be printed?
The answer is: 3 .
This is about initialization. After the first inner loop is executed, j = 3. At this time, when the inner loop is executed for the second time, j is still 3 because j has not been initialized to a certain number. , so if the judgment condition is not satisfied, it will not be executed.
int i = 0;
for (i = 0; i = 1; i++)
{
printf("hehe");
}
How many "hehe" will be printed for such a code?
The answer is: countless, infinite loop printing .
It should be noted that i = 1 here , is it a judgment statement? No, it is actually an assignment statement , and it assigns 1 to i , so the judgment condition is always true , and it will print in an endless loop.
3. The two major keywords in the loop
1.continue
continue , its English meaning is "continue" , when it is used in a loop statement, it will immediately end the current loop , stop the execution of the following statement and restart the loop .
#include<stdio.h>
int main()
{
int i = 1;
while (i <= 10)
{
printf("%d", i);
if (i == 5)
continue;
i++;
}
return 0;
}Looking at the above code, what will be the output of this code?
Did you guess right?
That's right, after printing 1,2,3,4 , it will print 5 in an infinite loop . why? When we meet the condition of i==5 , the if statement will be executed, and continue will be a demon at this time , it directly terminates the execution of i++ later , and restarts the cycle . At this time, i is always 5 , and it will always Execute continue , i will no longer be ++, so it will print 5 in an endless loop.
2.break
break , its English meaning is "break" , when it appears in a loop statement, no matter where it is, as long as it is shot, it will directly break the entire loop , the entire loop will not be executed , and the statement behind the loop will be executed directly .
#include<stdio.h>
int main()
{
int i = 1;
while (i <= 10)
{
printf("%d ", i);
if (i == 5)
break;
i++;
}
printf("循环被打破了");
return 0;
}The same code, what will it output?
Yes, when we print to 5 in the loop , the if statement executes, break it , and directly end the entire loop after i = 5 , and then execute the printf statement after the loop .
This knowledge sharing about circulation is coming to an end here. If you have any questions or additions to my sharing, please feel free to comment and send me a private message.
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