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;
}