为什么string哪里报错了？怎么改呀！（大佬救命！！！）

#include<stdio.h>
#include<string.h>
int main()
{
    int n, i, j;
    char a[1005];
    string ans[6];
    scanf("%d", &n);
    for (i = 1; i <= n; i++)
    {
        a[i] = getchar();
        if (a[i] == '1')
        {

            ans[1] += "..X.";
            ans[2] += "..X.";
            ans[3] += "..X.";
            ans[4] += "..X.";
            ans[5] += "..X.";
        }
        if (a[i] == '2')
        {
            ans[1] += "XXX.";
            ans[2] += "..X.";
            ans[3] += "XXX.";
            ans[4] += "X...";
            ans[5] += "XXX.";
        }
        if (a[i] == '3')
        {
            ans[1] += "XXX.";
            ans[2] += "..X.";
            ans[3] += "XXX.";
            ans[4] += "..X.";
            ans[5] += "XXX.";
        }
        if (a[i] == '4')
        {
            ans[1] += "X.X.";
            ans[2] += "X.X.";
            ans[3] += "XXX.";
            ans[4] += "..X.";
            ans[5] += "..X.";
        }
        if (a[i] == '5')
        {
            ans[1] += "XXX.";
            ans[2] += "X...";
            ans[3] += "XXX.";
            ans[4] += "..X.";
            ans[5] += "XXX.";
        }
        if (a[i] == '6')
        {
            ans[1] += "XXX.";
            ans[2] += "X...";
            ans[3] += "XXX.";
            ans[4] += "X.X.";
            ans[5] += "XXX.";
        }
        if (a[i] == '7')
        {
            ans[1] += "XXX.";
            ans[2] += "..X.";
            ans[3] += "..X.";
            ans[4] += "..X.";
            ans[5] += "..X.";
        }
        if (a[i] == '8')
        {
            ans[1] += "XXX.";
            ans[2] += "X.X.";
            ans[3] += "XXX.";
            ans[4] += "X.X.";
            ans[5] += "XXX.";
        }
        if (a[i] == '9')
        {
            ans[1] += "XXX.";
            ans[2] += "X.X.";
            ans[3] += "XXX.";
            ans[4] += "..X.";
            ans[5] += "XXX.";
        }
        if (a[i] == '0')
        {
            ans[1] += "XXX.";
            ans[2] += "X.X.";
            ans[3] += "X.X.";
            ans[4] += "X.X.";
            ans[5] += "XXX.";
        }
    }
    ans[1] -= '.';
   ans[2] -= '.';
    ans[3] -= '.';
    ans[4] -= '.';
    ans[5] -= '.';
    for (j = 1; j <= 5; j++)
    {
        printf("%s", ans[j].c_str());
        if (j != 5)printf("\n");
    }
    return 0;
}