1.登录账号密码

void sign_in(FILE *fp)//注册
{
	char usrname[10];
	char pwd[12];
	printf("输入账户:");
	scanf("%s",usrname);
	printf("输入密码:");
	scanf(" %s",pwd);
	fprintf(fp,"%s %s\n",usrname,pwd);
	printf("注册成功\n");
}

int main(int argc, const char *argv[])
{
	FILE *fp=fopen("./information.txt","a+");
	/*sign_in(fp);
	sign_in(fp);
	sign_in(fp);
	fclose(fp);
*/  char usrname[10];
	char pwd[12];//文件中的用户密码
	char Uname[10];
	char Pword[12];//要登录的用户密码
	fp=fopen("./information.txt","r");
	printf("输入账户:");
	scanf("%s",Uname);
	printf("输入密码:");
	scanf("%s",Pword);
	int j=-1;
	while(fscanf(fp,"%s %s",usrname,pwd)!=EOF)
	{
		if(strcmp(usrname,Uname)==0&&strcmp(pwd,Pword)==0)
		{
			printf("登陆成功\n");
			j=0;
			break;
		}
		else if(strcmp(usrname,Uname)==0&&strcmp(pwd,Pword)!=0)
		{
			printf("密码错误\n");
			j=1;
			break;
		}
	}
	if(j!=0&&j!=1)
	{
		printf("账户不存在\n");
	}
	fclose(fp);
	return 0;
}

2.计算文件字符数，行数

#include <myhead.h>
void count(FILE *fp)
{
	int count1=0;
	int count2=0;
	while(1)
	{
		char c=fgetc(fp);
		if(c==EOF)
		{
			break;
		}
		count1++;
		if(c=='\n')
		{
			count2++;
		}
	}
	printf("字符个数=%d\n",count1);
	printf("行数=%d\n",count2);
}
int main(int argc, const char *argv[])
{
	FILE *fp=fopen("./1.txt","r");
	count(fp);
	fclose(fp);
	return 0;
}

3.xmind