C program fragment to demonstrate how the standard input of a process may be redirected away from the terminal keyboard to a file

Question

I have a question: How C program fragment to demonstrate how the standard input of a process may be redirected away from the terminal keyboard to a file.

Am very new to C. I have given a lot of my time and tried until here. Not sure how to proceed further. Can someone please guide me on this?

#include <stdli.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <string.h>
#include <stdio.h>


int main(){
    int fd;
    char str[255];

    fd = open ("foo", O_WRONGLY | O_CREATE, 0766);

    if (fd==-1){
        perror("Error inopening the file ");
        exit(1);
    }
     printf("Enter a string: ");
     fgets(str, sizeof(str), stdin);
     dup2(fd, STDOUT_FILENO);
     .......
     ...
     exit(0);
}