15-4从键盘上输入字符串送到文件fiel1.txt中，然后再从该文件中读出所有的字符串。采用fprintf

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define nu NULL
int main()
{
	FILE *fp;
	char string[81];
	if((fp=fopen("file1.txt","w"))==nu)
	{
		printf("cannot open this file");
		exit(0);
	}
	while(strlen(gets(string))!=nu)
		{
			fputs(string,fp);
			fprintf(fp,"\n");
	}
	fclose(fp);
	if((fp=fopen("file1.txt","r"))==nu)
	{
		printf("cannot open this file");
		exit(0);
	}
	else {
		while(fgets(string,18,fp)!=nu)
		{
			printf("%s",string);
		}
		fclose(fp);
	}
}