[C language - zero foundation lesson 8] circular structure and break continue

Preface

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This issue is about C Language cycle structure and break continue, If there is any mistake, you are welcome to put forward your views .

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Catalog

while() Loop statement

do-while sentence

for（） Loop statement

Break and continue

Break sentence

continue sentence

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    The most important thing in life is circulation , The earth goes around the sun 、 a week 7 God 、 One day 24 Hours 、 An hour 60 Minutes, this is the cycle . stay C There are also cycles in language . If I let you use C Language promises 100 strip “ I like C Language ”, What method would you choose , I don't think you want to play 100 strip print(“ I like C Language \n”); Too tired , And no brain . So the circular structure we learn is used to solve this problem , Loop statements have while、do-while、for.

while() Loop statement

Format

While（ Conditions ）{

sentence ;

}

conditions for execution ： Judge the conditions first , When the condition is true, the loop statement is executed , End the loop until the condition is false .

int i = 1;
	while (i<=10)
	{
		printf("%d",i);
		i++;
	}

result ：12345678910

There are three elements of circulation ： The initial value of the cycle 、 The loop condition 、 Cycle increment （ Step value ）

do-while sentence

Format ：do sentence

While（ Conditions ）;

Execution process ： Execute statement first , In judging conditions , When the condition is true, continue to execute the loop statement , Until the condition is false .

int i = 1;
	do
		printf("%d", i);
		while (i>5);

result ：1

int i = 1;
	do 
    printf("%d",i++);
		while (i<5);

result ：1234   i++ The post value usage is used  

Do-while and while The difference between loop statements

Do-while Execute the loop at least once ,while The statement may not be executed once .

Do-while The end sign of the loop statement is ;

for（） Loop statement

Format

For（ Conditions for a ： initial value ; Condition 2 ： Conditions ; Condition 3 ： The incremental ）{

sentence ;

}

for ( int i = 0;  i <= 100;  i++)
	{
		printf("%d\n",i);
	}

result ：  Print out 0-100 Value

Calculation 1-100 Summation of

int sum = 0;

	for ( int i = 1;  i <= 100;  i++)
	{
		sum += i;
	}
	printf("1-100 The cumulative sum of is %d",sum);

  result ： 1-100 The cumulative sum of is 5050

For The characteristics of the cycle ： It is mostly used to specify the initial value and known termination conditions 、 The number of cycles is controllable

Get into for Loop executes the statement of loop one first （ stay for Only execute once in the loop ）, Then judge the conditions , If it's true, it goes into a cycle , Then execute condition 3 next time —— Whether condition two is true, and then in this order , Until the conditions don't hold .

Break and continue

Break sentence

Break sentence ： Jump out and terminate the current loop .

No, break The sentence of

for (int i = 1;i <= 5;i++) {
		printf("%d\n",i);
	}

  result ：

1
2
3
4
5

Yes break The sentence of

stay for In circulation

for (int i = 1;i <= 5;i++) {
		printf("%d\n",i);
		break;
	}

  result ：

1

The program only executes once and jumps out of the loop ;

for (int i = 1;i <= 5;i++) {
		if (i == 3) {
			break;
		}

		printf("%d\n",i);
		
	}

  result ：

1

2

The program only executes until the judgment condition is established and directly jumps out for loop ;

stay while In circulation

int i = 1;
	while (1) {// Not 0 It's all true , therefore while The condition is always true 
		if (i > 5) { i>5  sign out while loop 
			break;
		}
		printf("%d\n",i++);
	}

  result ：

1

2

3

4

5

stay switch In circulation

We can use break Calculate the number of days per month , Because in switch There is no break Just keep going , Until I met break stop it .

int i ;
	scanf("%d",&i);
	switch (i)
	{
	case 1:
	case 3:
	case 5:
	case 7:
	case 8:
	case 10:
	case 12: printf("31");break;
	case 2:
	case 4:
	case 6:
	case 9:
	case 11:printf("30");break;
	default:
		printf("28 or 29");
		break;
	}

continue sentence

continue： End this cycle and proceed to the next cycle

stay for In circulation

for (int i = 0;i <= 5;i++) {
		if (i == 4)continue;
		printf("%d",i);
	}

result ：01235

stay while In circulation

int i = 0;
	while (i++<5)
	{
		if (i == 4)continue;
		printf("%d",i);
	}

result ：1235

continue： Do not use... In selection statements （switch sentence ）, Use only in loop statements .

A nested loop

What is nesting ： A circular sentence contains another circular sentence , For example, you are watching TV now and the people on the TV screen are watching TV .

example 1：

for (int i = 0; i < 2; i++){
		for (int  j = 0; j < 1; j++)
		{
			printf("%d,%d\n", i, j);
		}
	}

  result ：

0,0
1,0

analysis ： We can see the first output 0,0 That is, execute the outer layer first for loop i=0, Then enter the inner layer for loop i=0, Output 0,0 Then the inner layer for loop j+1 be equal to 1,1<1 If the condition is not satisfied, the execution will be executed for loop ,i=1; Then the inner layer for loop j=0 Then the output 1,0 Then the inner layer for The cycle is equal to 1 Exit if the conditions are not met for loop i=2 Exit the loop if the conditions are not met .

  example 2：

for (int i = 0; i < 1; i++){
		for (int  j = 0; j < 5; j++)
		{
			if (i == 3) {

				break;
			}
			printf("j=%d\n", j);
		}
		printf("i=%d\n", i);
	}

result ：

j=0
j=1
j=2
j=3
j=4
i=0

break; A statement is to jump out of the nearest for Cyclic .

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