1，思维导图

2，登录

#ifndef __LOG_H__
#define __LOG_H__
#include<myhead.h>
typedef struct
{
	char name[20];
	char pwd[20];
}str;


int regist();

int login();
#endif

#include"log.h"
int login()
{
	char a[20]="\n";
	str p,s;
	printf("输入登录账户：");
	fgets(p.name,sizeof(p.name),stdin);
	printf("输入登录密码：");
	fgets(p.pwd,sizeof(p.pwd),stdin);

	printf("%ld%ld",strlen(p.name),strlen(p.pwd));

//	p.name[strcspn(p.name,"\n")]='\0';
//	p.pwd[strcspn(p.pwd,"\n")]='\0';

	FILE *fp=fopen("./user.txt","r");

	fscanf(fp,"%s%s",s.name,s.pwd);
	strcat(s.name,"\n");
	strcat(s.pwd,"\n");
	if(strcmp(p.name,s.name)==0
			&&
	   strcmp(p.pwd,s.pwd)==0)
	{
		printf("登录成功！！！\n");
	}
	else
	{
		printf("登录失败！！！\n");
	}
	return 0;
}

#include"log.h"
int regist()
{
	str s;
	FILE *fp=fopen("./user.txt","w");
	if(fp==NULL)
	{
		perror("fopen");
		return -1;
	}
	
	printf("建立新账户：");
	fgets(s.name,sizeof(s.name),stdin);
	printf("建立新密码：");
	fgets(s.pwd,sizeof(s.pwd),stdin);
	
	fprintf(fp,"%s%s",s.name,s.pwd);
	
	fclose(fp);
	
	printf("注册成功！！！\n");
	
	return 0;
}

#include"log.h"
int main()
{
	int n;
	while(1)
	{
		printf("1.注册账户\n");
		printf("2.登录账户\n");
		printf("3.退出\n");
		printf("请选择：");
		scanf("%d",&n);
		getchar();
		switch(n)
		{
		case 1:regist();break;
		case 2:login();break;
		case 3:exit(0);
		}
	}
	return 0;
}

3，复制

#include<myhead.h>
int main(int argc, const char *argv[])
{
	FILE *fp1=fopen("./1.txt","r");
	FILE *fp2=fopen("./2.txt","w");
	char str[5];
	while(1)
	{
		fread(str,sizeof(str),1,fp1);
		if(feof(fp1))
		{
			printf("读取成功！！！\n");
			break;
		}
		else if(ferror(fp1))
		{
			printf("读取失败！！！\n");
			break;
		}
		fwrite(str,sizeof(str),1,fp2);
	}
	fclose(fp1);
	fclose(fp2);
	fp2=fopen("./2.txt","r");
	while(fgets(str,sizeof(str),fp2))
	{
		fputs(str,stdout);
	}
	fclose(fp2);
	putchar(10);
	return 0;
}