Lab46 Wiki

Original code:

#include<stdio.h>
 
int main()
{
    int a, b, c, d;
    float avg;
 
    printf("Please enter the first number: ");
    scanf("%d", &a);
 
    printf("Please enter the second number: ");
    scanf("%d", &b);
 
    printf("Please enter the third number: ");
    scanf("%d", &c);
 
    printf("Please enter the fourth number: ");
    scanf("%d", &d);
 
    avg = (float)(a + b + c + d) / 4;      // force operation to be considered float, not native (int)
    printf("The average is %.2f\n", avg);  // format to 2 decimal places with the .2
 
    return(0);
}

With this code typed in, compiled, and ran, you can manually enter the 4 values and should see their average.

Conversely, we can also put our desired input in a file and feed in into our program via I/O redirection:

lab46:~/src/unix$ echo 24 > infile
lab46:~/src/unix$ echo 37 >> infile
lab46:~/src/unix$ echo 16 >> infile
lab46:~/src/unix$ echo 29 >> infile
lab46:~/src/unix$ cat infile
24
37
16
29
lab46:~/src/unix$ ./avgprog < infile

Output may seem a little messy, but that's only because it still expects actual enter keys to be hit. Notice the desired end result IS displayed.

Identical code, minus a lie:

#include<stdio.h>
 
int main()
{
    int a, b, c, d;
    float avg;
 
    fprintf(stdout, "Please enter the first number: ");
    fscanf(stdin, "%d", &a);
 
    fprintf(stdout, "Please enter the second number: ");
    fscanf(stdin, "%d", &b);
 
    fprintf(stdout, "Please enter the third number: ");
    fscanf(stdin, "%d", &c);
 
    fprintf(stdout, "Please enter the fourth number: ");
    fscanf(stdin, "%d", &d);
 
    avg = (float)(a + b + c + d) / 4;      // force operation to be considered float, not native (int)
    fprintf(stdout, "The average is %.2f\n", avg);  // format to 2 decimal places with the .2
 
    return(0);
}

Basically, a regular printf() is IDENTICAL to an fprintf() to stdout. Everything is a file, remember?

Same deal with scanf()/fscanf() from stdin. The lowercase stdin/stdout/stderr are file pointers available to us in C.