I am getting the error "expression must have a constant value" in the line " int L[m + 1][n + 1]; ". Can you please help me out

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <vector>
using namespace std;

int max(int a, int b);
int lcs(char *X, char *Y, int m, int n)
{
	int L[m + 1][n + 1];
	int i, j;