Trouble With C++ Calculator, Exponents.?

Wow, I thought I had already posted this... But I guess not. Ok, so I made a revised calc, but it can't do exponents. Help, it just pauses, and sits there stupid.

Heres the source:

#include <iostream>

#include <string>

using namespace std;

double add(double, double);

double subtract(double, double);

double multiply(double, double);

double divide(double, double);

double expo(long long, double);

double tryagain();

double enternew();

string put1();

string put2();

string put3();

string put4();

string yn();

void do1();

void aaa();

int main()

{

aaa();

}

double add(double a, double b)

{

double c=(a+b);

return (c);

}

double subtract(double a, double b)

{

double c=(a-b);

return (c);

}

double multiply(double a, double b)

{

double c=(a*b);

return (c);

}

double divide(double a, double b)

{

double c=(a/b);

return (c);

}

double expo(double a, double b)

{

double x=1;

double q=a;

double yes;

while(x<b)

{

yes=(a+q);

}

return (yes);

}

string put1()

{

string a="Please input the first number.\n";

return (a);

}

string put2()

{

string a="Please input the second number.\n";

return (a);

}

string put3()

{

string a="Please try again.\n";

return (a);

}

string put4()

{

string a="Would you like to go again?\n";

return (a);

}

string yn()

{

string c;

cin >> c;

string a=c;

return (a);

}

void do1()

{

string q=put4();

cout << q;

string std=yn();

string a="yes";

string b="no";

if(std==a)

{

aaa();

}

if(std==b)

{

cout << "Ok then, guess there's always next time, eh?\n";

}

}

void aaa()

{

double a, b, x, y, z;

string c="add";

string d="subtract";

string e="multiply";

string f="divide";

string g="expo";

string h, i, j, k, l, m, n, o, p, q, r;

cout << "Please enter what you want to do.\n";

cin >> h;

if(h==c)

{

i=put1();

cout << i;

cin >> a;

i=put2();

cout << i;

cin >> b;

z=add(a,b);

cout << z << "\n";

}

if(h==d)

{

i=put1();

cout << i;

cin >> a;

i=put2();

cout << i;

cin >> b;

z=subtract(a,b);

cout << z << "\n";

}

if(h==e)

{

i=put1();

cout << i;

cin >> a;

i=put2();

cout << i;

cin >> b;

z=multiply(a,b);

cout << z << "\n";

}

if(h==f)

{

i=put1();

cout << i;

cin >> a;

i=put2();

cout << i;

cin >> b;

z=divide(a,b);

cout << z << "\n";

}

if(h==g)

{

i=put1();

cout << i;

cin >> a;

i=put2();

cout << i;

cin >> b;

z=expo(a,b);

cout << z << "\n";

}

if(h!=c && h!=d && h!=e && h!=f && h!=g)

{

cout << "Please try again, the statement you entered is invalid.\n";

aaa();

}

do1();

}

Thanks. Hope you can help.