problema 3 4bac

int a[50][50], m, n, i, j, k, s=0;
    cout<<"n="; cin>>n;
    cout<<"m="; cin>>m;
    for(i=1; i<=n; i++)
        for(j=1; j<=m; j++)
            cin>>a[i][j];
    cout<<"Introduceti un numar cuprins intre 0 si n"; cin>>k;
        for(j=1; j<=m; j++)
        {
            if(a[k][j]>0)
               s=s+a[k][j];
        }
    uc=s%10;
    cout<<uc;