C language: write code to implement, simulate the user login scenario, and only log in three times

topic:

Write code to simulate the user login scenario , and can only log in three times .

                 

Only three passwords are allowed ,

If the password is correct , the login is successful .

If the input is wrong three times , the program exits .

                    

 =========================================================================

                       

Ideas:

general idea:

(1). Generate related variables and character arrays for storing input data ,

Then set a variable flag to make it easier to judge whether the passwords are consistent later .

If it is consistent , change the flag to 1 , and if it is inconsistent , it will still be 0 .

              

(2). Use the for loop to input data three times .

                     

(3). Set the if condition judgment statement in the for loop to judge the data three times in a loop .

                   

(4). After jumping out of the for loop , check the variable flag and print the exit program information .

                

---

                 

first step:

(1). Generate relevant variables .

            

(2). Generate a character array to store the input data .

                 

(3). Set a variable flag ,

It is convenient to judge whether the password is consistent later ,

If it is consistent , change the flag to 1 , and if it is inconsistent , it will still be 0 .

                     

Implementation code:

#include <stdio.h>
int main()
{
	//生成相关变量：
	int i = 0; //循环变量

	//生成存放输入数据的字符数组
	char password[20] = { 0 };

	//设置一个变量flag：
	int flag = 0;


	return 0;
}

Realize the picture:

                 

---

                 

Step two:

(1). Use the for loop to input data three times .

                      

(2). The input string can be used: scanf("%s", password);

Because password is the name of the array and the first address of the array , there is no need to add the address character & .

                     

Implementation code:

#include <stdio.h>
int main()
{
	//生成相关变量：
	int i = 0; //循环变量

	//生成存放输入数据的字符数组
	char password[20] = { 0 };

	//设置一个变量flag：
	int flag = 0;

	//使用for循环，循环输入三次数据：
	for (i = 0; i < 3; i++)
	{
		//输入前先打印提示信息：
		printf("请输入密码：");
		//输入数据：
		scanf("%s", password);
		//因为password是数组，数组名是数组首地址，所以不用取地址符&


	}

	return 0;
}

Realize the picture:

                 

---

                 

third step:

(1). Set the if condition judgment statement in the for loop to judge the data three times in a loop .

             

(2). Determine whether the passwords ( strings ) are equal :

               

You cannot use == (equal to) to compare two strings , you should use

strcmp(Character array name, "string to compare")

For library functions , a header file needs to be added :  <string.h> .

                      

strcmp returns 0 : indicating that the two strings are equal ;

strcmp returns a number >0 : indicating that the first string is greater than the second string ;

strcmp returns a number <0 : indicating that the first string is less than the second string .

                 

String comparison size : the comparison is the ASCII value of the character at the corresponding position .

like:

Comparison of abcd and abq :

First digit : a == a

Second bit : b == b

Third place : c < q 

The ASCII value of c is less than the ASCII value of q

So abcd < abq

             

(3). If the password is correct , print the corresponding information , set the flag to 1 , and use break to break out of the loop .

              

(4). If the password is wrong , print the corresponding information .

                     

Implementation code:

#include <stdio.h>
#include <string.h>
int main()
{
	//生成相关变量：
	int i = 0; //循环变量

	//生成存放输入数据的字符数组
	char password[20] = { 0 };

	//设置一个变量flag：
	int flag = 0;

	//使用for循环，循环输入三次数据：
	for (i = 0; i < 3; i++)
	{
		//输入前先打印提示信息：
		printf("请输入密码：");
		//输入数据：
		scanf("%s", password);
		//因为password是数组，数组名是数组首地址，所以不用取地址符&

		//设置if条件判断语句循环判断三次数据
		if (strcmp(password, "123456") == 0)
			//假设密码是 123456 ，如果相等会返回 0，说明输入的和密码相同
		{
			printf("登录成功\n");
			flag = 1;
			break; //成功则跳出循环
		}
		else
		{
			printf("密码错误\n");
		}
	}

	return 0;
}

Realize the picture:

                 

---

                 

the fourth step:

After jumping out of the for loop , check the variable flag and print the exit program information .

                     

Implementation code:

#include <stdio.h>
#include <string.h>
int main()
{
	//生成相关变量：
	int i = 0; //循环变量

	//生成存放输入数据的字符数组
	char password[20] = { 0 };

	//设置一个变量flag：
	int flag = 0;

	//使用for循环，循环输入三次数据：
	for (i = 0; i < 3; i++)
	{
		//输入前先打印提示信息：
		printf("请输入密码：");
		//输入数据：
		scanf("%s", password);
		//因为password是数组，数组名是数组首地址，所以不用取地址符&

		//设置if条件判断语句循环判断三次数据
		if (strcmp(password, "123456") == 0)
			//假设密码是 123456 ，如果相等会返回 0，说明输入的和密码相同
		{
			printf("登录成功\n");
			flag = 1;
			break; //成功则跳出循环
		}
		else
		{
			printf("密码错误\n");
		}
	}

	//跳出 for循环 后，看变量flag情况打印退出程序信息。
	if (flag == 0)
	{
		printf("退出程序");//密码错误 则 退出程序
	}

	return 0;
}

Realize the picture:

                    

Final code and implementation effect

Final code:

#include <stdio.h>
#include <string.h>
int main()
{
	//生成相关变量：
	int i = 0; //循环变量

	//生成存放输入数据的字符数组
	char password[20] = { 0 };

	//设置一个变量flag：
	int flag = 0;

	//使用for循环，循环输入三次数据：
	for (i = 0; i < 3; i++)
	{
		//输入前先打印提示信息：
		printf("请输入密码：");
		//输入数据：
		scanf("%s", password);
		//因为password是数组，数组名是数组首地址，所以不用取地址符&

		//设置if条件判断语句循环判断三次数据
		if (strcmp(password, "123456") == 0)
			//假设密码是 123456 ，如果相等会返回 0，说明输入的和密码相同
		{
			printf("登录成功\n");
			flag = 1;
			break; //成功则跳出循环
		}
		else
		{
			printf("密码错误\n");
		}
	}

	//跳出 for循环 后，看变量flag情况打印退出程序信息。
	if (flag == 0)
	{
		printf("退出程序");//密码错误 则 退出程序
	}

	return 0;
}

Realize the effect:

Summarize:

Learn the use of strcmp() library function :

It is used to judge whether two strings are equal , and a header file needs to be added :  <string.h> .

                      

strcmp(Character array name, "string to compare")

                   

strcmp returns 0 : indicating that the two strings are equal ;

strcmp returns a number >0 : indicating that the first string is greater than the second string ;

strcmp returns a number <0 : indicating that the first string is less than the second string .

                 

String comparison size : the comparison is the ASCII value of the character at the corresponding position .