How to pass arrays into functions in C ( on Fedora )? - c

Question

Since I am a beginner have been practicing passing arrays as parameters to functions. Could someone explain why this program I wrote works fine on codeblox, but doesn't work in Fedora terminal (on Fedora it doesn't work for any number of scores). I'm using the GCC compiler.
#include<stdio.h>
int num,scores[]={},count,max,sum;
void input(int scores[]);
int findmax(int scores[]);
int findsum(int scores[]);
void display(int max,int sum);
int main()
{
printf("Enter number of scores\n");
scanf("%d",&num);
input(scores);
max=findmax(scores);
sum=findsum(scores);
display(max,sum);
return 0;
}
void input(int scores[])
{
for(count=0; count<num; count ++)
{
printf("Enter score #%d:\n",count);
scanf("%d",&scores[count]);
}
}
int findmax(int scores[])
{
for(count=0; count<num ; count ++)
{
if(scores[count]>max)
{
max=scores[count];
}
}
return max;
}
int findsum(int scores[])
{ sum=0;
for(count=0; count<num ; count++ )
{
sum=sum+scores[count];
}
return sum;
}
void display(int max,int sum)
{
printf("The max score is :%d\nThe total score is:%d\n",max,sum);
}

Answer 1

You should avoid using global variables unless they are absolutely required. None are required here. All values should be declared local to main and should be passed to each function as a parameter, as required.
You must validate ALL input by, at minimum, checking the return of scanf (or whatever input function you are using). If a user simply pressed Enter (generating a '\n') or enters words instead of numbers causing the conversion to fail, you are dead in the water and may well be watching an infinite loop scroll by until you kill the process. (a cat might step on the keyboard, etc.)
When using the scanf family of functions, if a failure occurs, you must account for any characters left in the input buffer (e.g. stdin with scanf). If scanf is called within a loop, you risk an infinite loop where the conversion fails, leaving the same characters in the input buffer only to be read again, and fail, over-and-over again.
If you do not validate your input, you can have no confidence that you are processing a valid input from that point forward, and may in fact be well off into Undefined Behavior. The scanf family of functions returns the number of valid conversions based on the number of format-specifiers contained within the format-string. So with "%d", you have one format-specifier (e.g. %d), so upon successful conversion the return will be 1 (you should also check for EOF if the user manually cancels input with Ctrl + d, or Ctrl + z on windoze -- which is left to you)
Putting those pieces together, you could do something like the following:
#include <stdio.h>
#include <limits.h> /* for INT_MIN */
#define MAX 512
void input (int *scores, int num);
int findmax (int *scores, int num);
int findsum (int *scores, int num);
void display (int max, int sum);
int main (void)
{
int num, scores[MAX] = { 0 }, max, sum;
printf ("Enter number of scores: ");
if (scanf ("%d", &num) != 1) { /* VALIDATE ALL input */
fprintf (stderr, "error: invalid integer input.\n");
return 1;
}
input (scores, num);
max = findmax (scores, num);
sum = findsum (scores, num);
display (max, sum);
return 0;
}
void input (int *scores, int num)
{
int count = 0;
while (count < MAX && count < num) { /* always protect array bounds */
printf ("Enter score [%d]: ", count);
while (scanf ("%d", &scores[count]) != 1) { /* VALIDATE input */
fprintf (stderr, "error: invalid input, try again.\n");
/* remove invalid chars from input buffer */
for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {}
goto badval;
}
count++;
badval:;
}
}
int findmax (int *scores, int num)
{
int max = INT_MIN, count;
for (count = 0; count < num; count++)
if (scores[count] > max)
max = scores[count];
return max;
}
int findsum (int *scores, int num)
{
int sum = 0, count;
for (count = 0; count < num; count++)
sum = sum + scores[count];
return sum;
}
void display (int max, int sum)
{
printf ("\nThe max score is :%d\nThe total score is:%d\n", max, sum);
}
Example Use/Output
$ ./bin/maxminsum
Enter number of scores: 5
Enter score [0]: 9
Enter score [1]: 3
Enter score [2]: 7
Enter score [3]: 8
Enter score [4]: 2
The max score is :9
The total score is:29
With Error Correction
$ ./bin/maxminsum
Enter number of scores: 5
Enter score [0]: 9
Enter score [1]: 3
Enter score [2]: foo
error: invalid input, try again.
Enter score [2]: 7
Enter score [3]: 8
Enter score [4]: bar
error: invalid input, try again.
Enter score [4]: 2
The max score is :9
The total score is:29
Leave a comment if you have further questions.