$
$ cat -n comparison.c
     1  // Compares four integers and prints which is greatest and which is smallest
     2
     3  #include <stdio.h>
     4
     5  int main(void)
     6  {
     7      int a, b, c, d;
     8
     9      // Prompts user to input four integers and stores in variables a, b
    10      // c and d
    11
    12      printf("Enter four integers: ");
    13      scanf("%d %d %d %d", &a, &b, &c, &d);
    14
    15      // to be the largest number among the numbers entered this number must
    16      // be strictly greater than all numbers entered
    17      // analogous for the smallest
    18
    19      // Test for number stored in variable a
    20      if ( a > b && a > c && a > d )
    21          printf("Greatest: %d\n", a);
    22      else if ( a < b && a < c && a < d )
    23          printf("Smallest %d\n", a);
    24
    25      // Test for number stored in variable b
    26      if ( b > a && b > c && b > d )
    27          printf("Greatest: %d\n", b);
    28      else if ( b < a && b < c && b < d )
    29          printf("Smallest %d\n", b);
    30
    31      // Test for number stored in variable c
    32      if ( c > a && c > b && c > d )
    33          printf("Greatest: %d\n", c);
    34      else if ( c < a && c < b && c < d )
    35          printf("Smallest %d\n", c);
    36
    37      // Test for number stored in variable d
    38      if ( d > a && d > b && d > c )
    39          printf("Greatest: %d\n", d);
    40      else if ( d < a && d < b && d < c )
    41          printf("Smallest %d\n", d);
    42
    43      return 0;
    44  }
    45
$
$

$
$ ./comparison
Enter four integers: 1 2 3 4
Smallest 1
Greatest: 4
$
$
$ ./comparison
Enter four integers: 18 44 7 31
Greatest: 44
Smallest 7
$
$