1> 使用fgets统计给定文件的行数

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	//定义文件指针
	FILE *fp=NULL;
	//打开文件（只读）
	if((fp=fopen("./test.txt","r"))==NULL)
	{
		perror("error fopen"); 
		return -1;
	}
	//定义数组
	char buf[10]="";
	//读取fp到buf中
	int i=0;
	while(1)
	{
		char *ptr=fgets(buf,sizeof(buf),fp);
		if(ptr==NULL)
		{
			break;
		}
		for(int j=0;j<10;j++)
		{
			if(buf[j]=='\n')
			{
				i++;
			}
		}
	}
	printf("n=%d\n",i);
	//关闭文件
	fclose(fp);
	return 0;
}

2> 使用fputs和fgets完成两个文件的拷贝

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	//定义文件指针
	FILE *fpr=NULL;
	if((fpr=fopen("./test.txt","r"))==NULL)
	{
		perror("fopen error");
			return -1;
	}
	FILE *fpw=NULL;
	if((fpw=fopen("./test1.txt","w"))==NULL)
	{
		perror("fopen error");
		return -1;
	}
	//定义数组
	char buf[10]="";
	//读取fpr到buf中
	while(1)
	{
		char *ptr=fgets(buf,sizeof(buf),fpr);
		if(ptr==NULL)
		{
			break;
		}
		fputs(buf,fpw);
	}
	fclose(fpr);
	fclose(fpw);
	return 0;
}

3> 完成注册登录功能

做个小菜单，功能1是注册功能，输入注册账户和注册密码，将账户和密码写入文件中。功能2是登录功能，提示并输入登录账户和登录密码，并用其遍历文件中的每一组账户和密码，如果匹配成功，则登录成功，如果全部不匹配则提示登录失败

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	int menu=0;
	while(1)
	{
		system("clear");
		printf("\t\t=====login interface=====\n");
		printf("\t\t=====1、register=====\n");
		printf("\t\t=====2、log in=====\n");
		printf("\t\t=====3、exit=====\n");
		printf("please enter options:");
		scanf("%d",&menu);
		getchar();
		switch(menu)
		{
		case 1:
			{
				//注册功能
				FILE *fp1=NULL;
				if((fp1=fopen("./ID.c","a"))==NULL)
				{
					perror("fopen error");
					return -1;
				}
				FILE *fp2=NULL;
				if((fp2=fopen("./passwd.c","a"))==NULL)
				{
					perror("fopen error");
					return -1;
				}
				printf("please enter your id:");
				char id[4]="";
				fprintf(fp1,"%s\n",id);
				printf("please enter your passwd:");
				char passwd[6]="";
				fprintf(fp2,"%s\n",passwd);
				printf("created successfully\n");
				fclose(fp1);
				fclose(fp2);
			}
			break;
		case 2:
			{
				//登录功能
				FILE *fp1=NULL;
				if((fp1=fopen("./ID.c","r"))==NULL)
				{
					perror("fopen error");
					return -1;
				}
				FILE *fp2=NULL;
				if((fp2=fopen("./passwd.c","r"))==NULL)
				{
					perror("fopen error");
					return -1;
				}
				printf("please enter your id:");
				char id[4]="";
				scanf("%s",id);
				char buf1[4]="";
				while(1)
				{
					fgets(buf1,sizeof(buf1),fp1);
					for(int i=0;i<sizeof(buf1);i++)
					{
						if(id[i]==buf1[i])
						{
							
						}
					}
				}
					char passwd[6]="";

			}
			break;
		case 3:goto END;
		default:printf("error options,please try again!\n");

		}
		//提示结束
		printf("please enter any key to end\n");
		while(getchar()!='\n');
	}
END:
	return 0;