使用fgets统计给定文件的行数

#include<stdio.h>
#include<string.h>
int main(int argc, const char *argv[])
{
	FILE *fp=NULL;
	if((fp=fopen("./test.txt","w"))==NULL)
	{
		perror("open err");
		return -1;
	}
	fputc('h',fp);
	fputc('\n',fp);
	fputc('e',fp);
	fputc('l',fp);
	fputc('\n',fp);
	fputc('\0',fp);
	fclose(fp);
	int line=0;
	if((fp=fopen("./test.txt","r"))==NULL)
	{
		perror("open err");
		return -1;
	}
	char ch=0;
	while(1)
	{
	   ch=fgetc(fp);
	  if(ch=='\n')
	  {
		  line++;
	  }
	  else if(ch==EOF)
	  {
		  line++;
		  break;
	  }
	}
	printf("%d\n",line);
	fclose(fp);
    return 0;
}

使用fputs和fgets完成两个文件的拷贝

#include<stdio.h>
#include<string.h>
int main(int argc, const char *argv[])
{
	FILE *fp=NULL;
	FILE *fp1=NULL;
	if((fp=fopen("./test.txt","w"))==NULL)
	{
		perror("open err");
		return -1;
	}
	fputs("hello",fp);
	fclose(fp);
	if((fp=fopen("./test.txt","r"))==NULL)
	{
		perror("open err");
		return -1;
	}
	char ch[1000]="";
	if((fp1=fopen("./test1.txt","w"))==NULL)
	{
		perror("open err");
		return -1;
	}
	while(1)
	{
		char *c=fgets(ch,sizeof(ch),fp);
	  if(c==NULL)
	  {
		  break;
	  }
	  else 
	  {
          fputs(ch,fp1);
	  }

	}
	fclose(fp);
	fclose(fp1);
    return 0;
}

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<string.h>
#include<stdlib.h>
int main(int argc, const char *argv[])
{
	FILE *fp=NULL;
	FILE *fp1=NULL;
	while(1)
	{
	printf("登录界面\n");
	printf("1.注册\n");
	printf("2.登录\n");
	printf("0.退出\n");
	int  meau=0;
	char username [10000]="";
	char password[10000]="";
	char username1[10000]="";
	char password1[10000]="";
	scanf("%d",&meau);
	switch(meau)
	{
	case 1:
		{
			printf("username:\n");
			scanf("%s",username);
			int lenname=strlen(username);
			if((fp=fopen("./username.txt","w"))==NULL)
			{
					puts("open err");
					return -1;
			}
			for(int i=0;i<lenname;i++)
			{
		       fprintf(fp,"%c",username[i]);
			}
			fclose(fp);
			printf("password:\n");
			scanf("%s",password);
			int lenpass=strlen(password);
			if((fp1=fopen("./password.txt","w"))==NULL)
			{
					puts("open err");
					return -1;
			}
			for(int i=0;i<lenpass;i++)
			{
			fprintf(fp1,"%c",password[i]);
		}
			fclose(fp1);
		}
		break;
	case 2:
		{
				printf("username:\n");
				scanf("%s",username);
				int lenname=strlen(username);
         			printf("password:\n");
		        	scanf("%s",password);
			int lenpass=strlen(password);
			if((fp=fopen("./username.txt","r"))==NULL)
			{
					puts("open err");
					return -1;
			}
			if((fp1=fopen("./password.txt","r"))==NULL)
			{
					puts("open err");
					return -1;
			}
			for(int i=0;i<lenname;i++)
			{
				fscanf(fp,"%c",&username1[i]);
			}
			for(int i=0;i<lenpass;i++)
			{
			fscanf(fp1,"%c",&password1[i]);
			}
			int len=lenname>lenpass?lenname:lenpass;
			for(int i=0;i<len;i++)
			{
			if (password[i]==password1[i]&&username[i]==username1[i])
			{
				if(i+1==len)
				{
				puts(username);
				puts(password);
				puts("success");
			}
			}
			else if (password[i]!=password1[i]&&username[i]!=username1[i])
			{
             puts("error");
			 break;
			}

		}
		}
		break;
	case 0:goto END;
	default:puts("input cd is error");
	}
	}
END:
	return 0;
}