Use a txt file to send input to my C program

#include<stdio.h>  

int main()   
{   
  int n, count = 1;   
  float x, average, sum = 0;   
  printf("How many numbers do you wish to test: ");  
  scanf ("%d",&n);   
  while (count <= n)   
     {   
      printf ("Enter number #%d: ",count);   
      scanf("%f", &x);   
      sum += x;   
      ++count;   
     }   
    average = sum/n;   
    printf("\nThe Average is: %.2f\n", average);   
}  

This program asks the user for a certain amount of numbers to be entered and then calculates the average of those numbers. My question is, if I want to use a file called inputfile.txt to input the data, how would I use redirection without typing in the data from STDIN? So instead the data comes from the inputfile.txt. Also how would I set up the inputfile.txt?

>Solution :

You’d put your numbers in a text file, one per line.

Then, because you need to enter the count first, use the wc command

$ gcc your_code.c

$ cat numbers
10
20
40

$ { wc -l < numbers; cat numbers; } | ./a.out
How many numbers do you wish to test: Enter number #1: Enter number #2: Enter number #3:
The Average is: 23.33

I use the braces to group the output of both wc and cat into a single input stream for your program.

A bash-specific technique: read the numbers from the file into a shell array, and then use printf to output the length of the array and the array elements.

$ readarray -t nums < numbers

$ printf '%d\n' "${#nums[@]}" "${nums[@]}" | ./a.out
How many numbers do you wish to test: Enter number #1: Enter number #2: Enter number #3:
The Average is: 23.33