Fix exercise 12.11 solution

[abdallahalsamman]

exercise 12.11 solution fails with this example

#include <stdio.h>
#include <stdbool.h>

int find_largest(int a[], int n) {

        int *p = a;
        int largest = *p++;

        while (p++ < a + n) {
                if (*p > largest) {
                        largest = *p;
                }
        }
        return largest;
}

int main(void) {
        int a[] = {1,4,2,3};
        printf("Largest number is: %d", find_largest(a, 4));
}

Expected result: Largest number is: 4
Actual result: Largest number is: 3