为啥编译错误？？？？？？？？？？？

#include <bits/stdc++.h>
#include<cstring>
#include<string>
using namespace std;

int main() {
	string a;
	int b, c, e;
	cin >> b;
    getline(cin,a);
	const char d, f;
	c = strlen(a);
	for (int i = 1; i <= c; i++) {
		d = a[i];
		e = d;
		e += b;
		f = e;
		cout << f;
	}
}