how to find the min/max of values within a file - c

Question

#include <stdio.h>
int main(void)
{
int num, i, total, average, min, max;
min = num;
max = num;
FILE *ifile;
ifile = fopen("scores.txt", "r");
i = total = 0;
while (fscanf(ifile, "%d", &num) != EOF) {
i++;
total += num;
}
printf("The total of the integers is %d.\n", total);
printf("The number of integers in the file is %d.\n", i);
average = total/i;
printf("The average of the integers is %d.\n", average);
while (fscanf(ifile, "%d", &num) != EOF) {
if (num < min) {
printf ("The minimum is %d\n", min);
} else if (num > max) {
printf ("The maximum is %d\n", max);
}
}
fclose(ifile);
return (0);
}
The part of the code that's wrong is the very end about mins/maxes.
I'm not sure whether to put in a loop for this or to even make min and max variables themselves.

Answer 1

There are at least three issues in your min/max-detection loop:
First, as indicated by chux, min and max are not initialized; hence, when iterating through the numbers, statement if (num < min)... is far from guaranteed to work properly (same for max, of course).
So initialize min with INT_MAX, and initialize max with INT_MIN (both defined in <limits.h>), such that already in the first iteration min and max will be set to values from your file.
Second, the check for if (num < min)... gives you a "local" minimum, i.e. the minimum for all the numbers read so far, but not the "absolute" minimum, as there may come smaller numbers at a later point. So min/max will be valid at the end of the loop, not during the iteration.
Third, if (num < min) ... else if (num > max) is wrong at least if the file contains just one number.
Your code could look like the following:
int min = INT_MAX;
int max = INT_MIN;
while (fscanf(ifile, "%d", &num) != EOF) {
if (num < min)
min = num;
if (num > max)
max = num;
}
// min/max are valid earliest at this point:
printf ("The minimum is %d\n", min);
printf ("The maximum is %d\n", max);
// Note that min/max will not be correct if the file does not contain any number;
// Note further, that fscanf(ifile, "%d", &num) != EOF may result in an endless loop if the file contains characters that "%d" will not read as a valid integral value.
// But this is left to the OP for further improvement :-)

Answer 2

Consider the following modification to your code:
#include <stdio.h>
int main(void) {
int num, i, total, average, min, max;
// open file
FILE *ifile = fopen( "scores.txt", "r" );
// if opening file fails, print error message and exit 1
if (ifile == NULL) {
perror("Error: Failed to open file.");
return 1;
}
// initialize i and total to zero.
i = total = 0;
// read values from file until EOF is returned by fscanf,
// or until an error (hence the comparison "== 1")
while(fscanf(ifile, "%d", &num) == 1) {
// In first round of loop, initialize min and max
// to the number being read (num)
// After min/max have been initialized, they can then
// be compared and modified in the second if statement
// in the remaining loop rounds
if (i == 0) {
min = num;
max = num;
total += num;
++i;
continue;
}
if (num < min) {
min = num;
} else if (num > max) {
max = num;
}
total += num;
++i;
}
// initialize average
average = total/i;
// summary
printf("The sum of all integers in file is %d.\n", total);
printf("The number of integers in file is %d.\n", i);
printf("The average of all integers in file is %d.\n", average);
printf ("The minimum is %d\n", min);
printf ("The maximum is %d\n", max);
fclose(ifile);
return 0;
}