p11.c

#include <stdio.h>

int main(void)
{

	int arr[20][20] = {
		{ 8, 2,22,97,38,15, 0,40, 0,75, 4, 5, 7,78,52,12,50,77,91, 8},
		{49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48, 4,56,62, 0},
		{81,49,31,73,55,79,14,29,93,71,40,67,53,88,30, 3,49,13,36,65},
		{52,70,95,23, 4,60,11,42,69,24,68,56, 1,32,56,71,37, 2,36,91},
		{22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80},
		{24,47,32,60,99, 3,45, 2,44,75,33,53,78,36,84,20,35,17,12,50},
		{32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70},
		{67,26,20,68, 2,62,12,20,95,63,94,39,63, 8,40,91,66,49,94,21},
		{24,55,58, 5,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72},
		{21,36,23, 9,75, 0,76,44,20,45,35,14, 0,61,33,97,34,31,33,95},
		{78,17,53,28,22,75,31,67,15,94, 3,80, 4,62,16,14, 9,53,56,92},
		{16,39, 5,42,96,35,31,47,55,58,88,24, 0,17,54,24,36,29,85,57},
		{86,56, 0,48,35,71,89, 7, 5,44,44,37,44,60,21,58,51,54,17,58},
		{19,80,81,68, 5,94,47,69,28,73,92,13,86,52,17,77, 4,89,55,40},
		{ 4,52, 8,83,97,35,99,16, 7,97,57,32,16,26,26,79,33,27,98,66},
		{88,36,68,87,57,62,20,72, 3,46,33,67,46,55,12,32,63,93,53,69},
		{ 4,42,16,73,38,25,39,11,24,94,72,18, 8,46,29,32,40,62,76,36},
		{20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74, 4,36,16},
		{20,73,35,29,78,31,90, 1,74,31,49,71,48,86,81,16,23,57, 5,54},
		{ 1,70,54,71,83,51,54,69,16,92,33,48,61,43,52, 1,89,19,67,48}	};


	int p = 0;
	int max = 0;
	int i, j;

	for (i = 0; i <= 16; i++) {
		for(j = 0; j <= 16; j++) {

			// Row
			p = arr[i][j] * arr[i][j+1] * arr[i][j+2] * arr[i][j+3];
			if (p > max)
				max = p;
	
			// Column
			p = arr[i][j] * arr[i+1][j] * arr[i+2][j] * arr[i+3][j];
			if (p > max)
				max = p;
			
			// Diagonal right
			p = arr[i][j] * arr[i+1][j+1] * arr[i+2][j+2] * arr[i+3][j+3];
			if (p > max)
				max = p;

			// Diagonal left
			p = arr[i][j+3] * arr[i+1][j+2] * arr[i+2][j+1] * arr[i+3][j];
			if (p > max)
				max = p;
	
		}
	}

	printf("%d\n", max);
	return(0);
}