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;