List of articles

Each preface

1. Introduction

2. The goal is

3. a key

while Loop statement

  1.1,while Sentence basic syntax

  1.2,while Recycling example

  1.3,while Precautions for use

  1.4,while Jump statement continue

  1.5,while Jump statement break

do-while Loop statement

  2.1,do-while Sentence basic syntax

  2.2,do-while Recycling example

  2.3,do-while Precautions for use

  2.4,do-while Jump statement continue

  2.5,do-while Jump statement break

for Loop statement

  3.1,for Sentence basic syntax

  3.2,for Recycling example

  3.3,for Precautions for use

  3.4,for Jump statement continue

  3.5,for Jump statement break

A nested loop

  4.1, Loop nesting basic syntax

  4.2, Examples of circular nesting

  4.3, Precautions for circular nesting

goto Jump statements

4. Conclusion

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Each preface

Blog home page ： Xiao Yang AI programming *

Author's brief introduction ：2022 Blog Mengxin in

My motto ： Those who have the will have the long will , He who has no will is determined to

The author requests ： Due to the limited level of bloggers , There will inevitably be mistakes and inaccuracies , I hope you can criticize me in the message area .

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Introduction

This blog mainly introduces you in detail C The circular structure of language . I hope you can read this blog , Benefit a lot ！

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The goal is

Understand and master C Knowledge of the circular structure of language , Have a new understanding and understanding of circular structure .

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Knowledge point

while Loop statement

1.1,while Sentence basic syntax

Sentence format ：

Execute the process ：

Process analysis ：

1. First step ： Evaluate the value of an expression , If the expression value is true , Go to step two , If it's false , Then jump to step 4 .
2. The second step ： Execute loop body statement .
3. The third step ： Step one back .
4. Step four ： End of cycle , perform while The next statement of a statement .

Be careful ：while Characteristics of sentences ： Execute the judgment condition first , Post execution loop body

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1.2,while Recycling example

Example ： Print 1-10 The number of

The code is as follows ：

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

Sample output ：

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1.3,while Precautions for use

1,while Parentheses after the statement "( )" Do not omit .

2,while The expression in the statement can be any type of expression , If the value of the expression is not 0, Indicates that the cycle condition is true , Execute loop body statement ; If the value of the expression is 0, Indicates that the cycle condition is false , Do not execute loop body statements , End of cycle , Execute the statement after the loop .

3, If the expression starts with 0, Then the loop body does not execute once , Directly execute the statement after the loop body .

4, The loop body statement can be a compound statement , That is, when the loop body is composed of multiple statements , The statement must be enclosed in a brace , Form compound statements .

5, In order for the cycle to end normally , The expression should be modified in the loop body , Make the value of the expression tend to be false , Avoid a dead cycle .

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1.4,while Jump statement continue

Examples are as follows ：

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

Sample output ：

Sample analysis :

In this while In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform continue sentence ,continue Statement will make this while Cycle termination ,continue The latter code does not execute , Direct transfer to while The judgment part of a sentence ,i Not in progress i++ operation ,i Always be 5, So this program will fall into an endless loop , The output results are printed out 1 2 3 4 Post dead cycle .

summary ：
1,continue Is used to terminate the cycle , In this cycle continue The following code is no longer executed , It's a jump to while The judgment part of a sentence . Make the entry judgment of the next cycle .

2,continue The sentence can only be in a circular sentence , Often with if Statements use .

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1.5,while Jump statement break

Examples are as follows ：

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

Sample output ：

Sample analysis :

In this while In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform break sentence ,break Statement will make this while Cycle termination , The following steps are not carried out , So this program will only print out 1 2 3 4.

Be careful ：i++ The position of this statement has an impact on the result of the program output , Different placement positions , The output results may be different .

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summary ：
1, When break Statement for while In loop statement , It can cause the program to terminate the loop and then execute while The statement follows the statement . In short , In the loop, whenever you encounter break, Just terminate the loop . therefore ：while Medium break It's used to terminate the loop permanently .

2, Usually ,break Sentences are always related to if Statements , That is, exit the cycle when the conditions are met .

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This returns the directory

do-while Loop statement

2.1,do-while Sentence basic syntax

Sentence format ：

Execute the process ：

Process analysis ：

1, First step ： Execute loop body statement .
2, The second step ： Evaluate the value of an expression , If the value of the expression is true （ Not 0）, Step one back ; If the value of the expression is false （0）, Then go to step three .
3, The third step ： End of cycle , perform do-while The next statement of a statement .

Be careful ：do-while The statement is characterized by executing the loop body first , Post judgment cycle conditions . therefore ,do-while The loop must be executed at least once .

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2.2,do-while Recycling example

Example ： Print 1-10 The number of

Sample code ：

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

Sample output ：

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2.3,do-while Precautions for use

1, stay do There can be no statement terminator after ";", Because the cycle is not over yet .

2, stay while（ expression ） After that, there must be a statement Terminator ";", Express do-while This is the end of the loop .

3, There must be a statement in the loop body to change the loop condition , Otherwise, there will be a dead cycle .

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2.4,do-while Jump statement continue

Sample code ：

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

Sample output ：

Sample analysis :

In this do-while In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform continue sentence ,continue Statement will make this do-while Cycle termination ,continue The latter code does not execute , Direct transfer to while The judgment part of a sentence ,i Not in progress i++ operation ,i Always be 5, So this program will fall into an endless loop , The output results are printed out 12 3 4 Post dead cycle .（ Use the same while The cycle is similar ）

Be careful ：i++ The position of this statement has an impact on the result of the program output , Different placement positions , The output results may be different .

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summary ：
1,continue Is used to terminate the cycle , In this cycle continue The following code is no longer executed , It's a jump to while The judgment part of a sentence . Make the entry judgment of the next cycle .

2,continue The sentence can only be in a circular sentence , Often with if Statements use .

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2.5,do-while Jump statement break

Examples are as follows ：

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

Sample output ：

Sample analysis :

In this do-while In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform break sentence ,break Statement will make this do-while Cycle termination , The following steps are not carried out , So this program will only print out 1 2 3 4.（ Use the same while The cycle is the same ）

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summary ：
1, When break Statement for do-while In loop statement , It can cause the program to terminate the loop and then execute while The statement follows the statement . In short , In the loop, whenever you encounter break, Just terminate the loop .

2, Usually ,break Sentences are always related to if Statements , That is, exit the cycle when the conditions are met .

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This returns the directory

for Loop statement

3.1,for Sentence basic syntax

Sentence format ：

Be careful :
expression 1 For the initialization part , Used to initialize loop variables .
expression 2 For the conditional judgment part , Used to determine whether the loop is terminated .
expression 3 For the adjustment part , For adjustment of cyclic conditions .

Execute the process ：

Process analysis ：

1. First step ： First calculate the expression 1.
2. The second step ： Judging expressions 2, If the value is true （ Not 0）, The loop body statement is executed , And then step three ; If it's false （0）, End of cycle , Go to step 5 .
3. The third step ： Calculation expression 3.
4. Step four ： Return to step 2 and continue .
5. Step five ： The loop ends , Carry on for The next statement of a statement .

Be careful ： expression 1 Just calculated once before entering the cycle . expression 2, Loop body statements and expressions 3 Will repeat .

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3.2,for Recycling example

Example ： Print 1-10 The number of

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

Sample output ：

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3.3,for Precautions for use

1, Omit expression 1, You can assign the initial value of the cyclic variable to for Before , But the first one cannot be omitted ";".

2, Omit expression 2, Indicates that the loop is not controlled , At this time, if there is no other treatment, there will be an dead cycle , This should be avoided .

3, Omit expression 3, You can add a statement that modifies the value of the loop variable to the loop body sentence .

4,for An expression in the general form of a statement 1 And expressions 3 It can be a comma expression .

5,for An expression in the general form of a statement 2 As long as the value of is not 0, Execute the loop body .

6,for The circular body statement in the general form of the statement can be omitted .

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3.4,for Jump statement continue

Sample code ：

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

Sample output ：

Sample analysis :

In this for In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform continue sentence ,continue Statement will make this for Cycle termination ,continue The latter code does not execute , Direct transfer to for The judgment part of the loop statement , Not printed 5 The operation of this number ,i Decide to proceed again according to the result of the judgment part i++ operation , In turn, print 6 7 8 9 10, So the final output of this program is to print out 1 2 3 4 6 7 8 9 10, The lack of 5.（ And while Circulation and do-while Circular usage is different ）

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summary ：
1,continue Is used to terminate the cycle , In this cycle continue The following code is no longer executed , It's a jump to while The judgment part of a sentence . Make the entry judgment of the next cycle .

2,continue The sentence can only be in a circular sentence , Often with if Statements use .

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3.5,for Jump statement break

Sample code ：

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

Sample output ：

Sample analysis :

In this for In circulation ,i from 1 After printing in turn ++. When the program prints 4 after , The program is executed again i++ After this code i The value of is 5, When i==5 when , perform break sentence ,break Statement will make this while Cycle termination , The following steps are not carried out , So this program will only print out 1 2 3 4.（ And while Circulation and do-while Circular usage is similar ）

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summary ：
1, When break Statement for while In loop statement , It can cause the program to terminate the loop and then execute while The statement follows the statement . In short , In the loop, whenever you encounter break, Just terminate the loop .

2, Usually ,break Sentences are always related to if Statements , That is, exit the cycle when the conditions are met .

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This returns the directory

A nested loop

4.1, Loop nesting basic syntax

Sentence format ：

• for Nested in statement for sentence
  

• for Nested in statement while sentence
  

• while Nested in statement while sentence
  

• do-while Nested in statement for sentence
  

• do-while Nested in statement do-while sentence
  

• while Nested in statement do-while sentence
  

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4.2, Examples of circular nesting

Example ： Print the multiplication table

Sample code ：

#include<stdio.h>
int main()
{ 
	for (int i = 1; i <= 9; i++)
	{
		for (int j = 1; j <= i; j++)
		{
			printf("%d*%d=%2d ",j , i,  i * j);
		}
		printf("\n");
	}
	return 0;
}  

Sample output ：

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4.3, Precautions for circular nesting

1, The outer loop is executed once , The inner loop executes a round .

2, The inner and outer loop bodies in the loop nested format are not allowed to cross , That is, the outer loop should completely include the inner loop .

3, Loop nesting , Used in internal circulation break Statement and continue When the sentence is , Only the inner loop containing them is affected , It has nothing to do with external circulation .

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This returns the directory

goto Jump statements

goto sentence ： You can abuse and mark jump at will . Theoretically goto Statements are not necessary , But on some occasions goto Statements are still useful , The most common use is to terminate the processing of a program's deeply nested structure .

for example ： Jump out of two or more loops at a time .

Multilayer loops are used in this case break Can't achieve the goal .break You can only exit from the innermost loop to the previous loop .

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This returns the directory

Conclusion

Dear friends ,【 Xiao Yang will show you around C Language 】 Loop structure （ Detailed explanation ） That's it , In the next issue, I will explain the function part to you . Coming soon ！

If you guys feel good about it , Or some harvest after reading , Please move your little hands , Give me a three company （ Focus on , give the thumbs-up , Comment on ）, Give me more support ！！
friends , Bear in mind ！ These sample code must remember to actually operate , Only in this way can we deepen our understanding of these knowledge ！

Last , Thank you for reading , Let's work together , Come on together , Progress together !

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