Write a C program that redirects standard output to a file output.txt. (use of dup and open system

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
int main(void) {
int number1, number2, sum;
int input_fds = open("./input.txt", O_RDONLY);
if(dup2(input_fds, STDIN_FILENO) < 0) {
printf("Unable to duplicate file descriptor.");
exit(EXIT_FAILURE);
}
scanf("%d %d", &number1, &number2);
sum = number1 + number2;
printf("%d + %d = %d\n", number1, number2, sum);
return EXIT_SUCCESS;
}