bai3.cpp

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

int main() {
  string s; char c;
  cout << "Nhap s: "; getline(cin, s);
  cout << "Nhap c: "; cin >> c;
  int pos = -1;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] == c && pos == -1) pos = i;
  }
  cout << "Vi tri dau tien chua ky tu c: " << pos << '\n';
}