C Program will compile and run in Linux but not Windows - c

Question

I'm working on an assignment for a programming class and am having an issue with a program. The goal is to take in a set of user defined values, store them in an array, then find the closest pair of numbers (the numbers with the smallest difference). The numbers don't have to have consecutive indices. Also, the array size of 50 is defined in the assignment by the professor.
The problem I'm running into is that the program will compile in both Linux (Ubuntu 14.xx) and Windows 10, however, when I run the result in Linux, it works fine but in Windows it outputs nothing.
This is the first time I've had this issue and as far as I know I didn't use any system specific commands. Any help provided would be appreciated.
Code:
#include <stdio.h>
int main()
{
int i, j, a, b, temp, mindiff, count;
int numarray[50];
count = 0;
for (i = 0; i < 50; i++)
{
scanf("%d", &numarray[i]);
count++;
if (numarray[i] == -1)
{
numarray[i] = 0;
count--;
break;
}
}
mindiff = 100;
for (i = 0; i < count; i++)
{
for (j = 0; j < count; j++)
{
a = numarray[i];
b = numarray[j];
if (a != b)
if (a > b)
temp = a - b;
else
temp = b - a;
if (temp < mindiff)
mindiff = temp;
}
}
for (i = 0; i < count; i++)
{
for (j = 0; j < count; j++)
{
a = numarray[i];
b = numarray[j];
if (a != b)
{
if (a > b && (a - b) == mindiff)
{
printf("Closest pair: %d and %d, Difference: %d\n", a, b, mindiff);
return 0;
}
}
}
}
return 0;
}

Answer 1

There are at least two major problems:
Your code has undefined behavior because you use temp even if it has not been set (you should start a block after if (a != b)). undefined behavior means anything can happen, including apparent success on Linux and failure on Windows.
You initialize mindiff to 100. If all numbers are farther apart from each other, mindiff will not be changed and the second loop will not print anything.
Here is a simpler version:
#include <stdio.h>
int main(void) {
int count, i, j, mina, minb, mindiff;
int numarray[50];
for (count = 0; count < 50; count++) {
if (scanf("%d", &numarray[count]) != 1 || numarray[count] == -1)
break;
}
mindiff = mina = minb = 0;
for (i = 0; i < count; i++) {
for (j = 0; j < count; j++) {
int a = numarray[i];
int b = numarray[j];
if (a > b) {
int diff = a - b;
if (mindiff == 0 || mindiff > diff) {
mindiff = diff;
mina = a;
minb = b;
}
}
}
}
if (mindiff == 0) {
if (count == 0) {
printf("No numbers input\n");
} else {
printf("The numbers are all identical\n");
}
} else {
printf("Closest pair: %d and %d, Difference: %d\n",
mina, minb, mindiff);
}
return 0;
}

Answer 2

You have the following problem:
Note: temp is considered a stack variable under the main function and since you do not initialize it, it becomes garbarge (for example a large negative number):
int i, j, a, b, temp, mindiff, count;
Then if temp is a large negative number, mindiff = the garbarge value of mindiff,
if (temp < mindiff)
mindiff = temp;
And the following if statement is always false.
if (a > b && (a - b) == mindiff)
And nothing gets printed.