c语言将字符串写入文件,并从文件中读取

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char arr[100];
    FILE *fp=fopen("a.tex","r+");
    printf("请输入一串字符给arr: ");
    gets(arr);
    fopen("a.tex","w");
    if(fp!=NULL){
        int i;
        for(i=0;i<strlen(arr);i++){
                fputc(arr[i],fp);
        }
    }
    fclose(fp);
    arr[0]='\0';
    printf("数组arr中的内容: ");
    fopen("a.tex","r");
    char ch;
    if(fp!=NULL)
    {

       ch=fgetc(fp);
       while(ch!=EOF)
       {
           printf("%c",ch);
           ch=fgetc(fp);
       }