std::string input;
cout << "Enter a percent";
getline(input, cin);
double n;
stringstream str(input);
str >> n;

#include <iostream>
#include <string>
 
using namespace std;
 
int main(void)
{
    string usrInput;
    double dbl = 0;
    cout << "Enter a percent: ";
 
    getline(cin, usrInput);
    cout << endl;
 
    if(usrInput.c_str()[usrInput.length()-1] == '%')
    {
        usrInput.replace(usrInput.length()-1, 0, "");
 
        cout << usrInput << endl;
 
        dbl = atof(usrInput.c_str());
    } else {
        dbl = atof(usrInput.c_str());
    }
 
    cout << "The double is: " << dbl << endl;
 
    return 0;
}

#include <iostream>
#include <sstream>
#include <string>
 
using namespace std;
 
int main(void)
{
    string str;
    double dbl = 0;
 
    cout << "Type a number: ";
    cin >> str;
    cout << endl;
    stringstream ss(str);
    ss >> dbl;
    cout << "The number is: " << dbl;
 
    return 0;
}

if(usrInput.c_str()[usrInput.length()-1]=='%')
...

if(usrInput[usrInput.length()-1] == '%')