it has all right answer and why access violation?



#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cmath>
int a[40][50];
using namespace std;
int main(){
    int n,i,j,k;

    cin>>n;
    a[0][0]=2;
    a[1][0]=2;
    if (n>1){
        for (i=2; i<n; i++){
            for (j=0; j<39; j++){
                a[i][j]=a[i-1][j]+a[i-2][j];
            }
            for (j=0; j<19; j++){
                a[i][j+1]+=a[i][j]/10;
                a[i][j]=a[i][j]%10;
            }
        }
    }
        for (i=39; i>-1; i--){
            if (a[n-1][i]>0){
                for (j=i; j>-1; j--){
                    cout<<a[n-1][j];
                }
                break;
            }

        }

        //system("pause");
}