#include <stdio.h>
#include <stdlib.h>

#define SIZE 4

void getInput(int num[]);
int getLargest(int num[], int size);

int main()
{
		int i, largest, num[SIZE];

		getInput(num);
		getLargest(num, SIZE);

		printf("The largest number is: %i. \n", getLargest(num, SIZE));

		system("pause");
		return 0;
}

void getInput(int num[])
{
	int i;

	for (i = 0; i < SIZE; i++)
		{
			printf("Enter a unique integer: ");
			scanf("%i", & num[i]);
		}
}

int getLargest(int num[], int size)
{
	int i, largest;

	for (i = 0, largest = num[i++]; i < SIZE; i++)
		{
			if (num[i] > largest)
			{
				largest = num[i];
			}
		}
	return largest;
}

Takes input from user, then gives back the largest number from input. Array size can easily be changed through the constant SIZE. Notice the functions at the bottom. 🙂