Ok. sorry to bother you guys with a newb question.

Ok ive just started learning c++. Acctualy i tried to start for like a year ago but I didnt have enough time to learn it.
Anyway. here is my problem.

"Write a program that asks for a number and a power. Write a recursive function that takes the number to the power. Thus, if the number is 2 and the power is 4, the function will return 16"

That is an exercise from my book.

So far i have this

Code:

---

#include <iostream>
#include <stdlib.h>

float myFunc(unsigned short int x, unsigned short int y);

int main()
{
unsigned short int x = 0;
unsigned short int y = 0;
float z;

std::cout<<"Write a exponent: ";
std::cin>>x;
std::cout<<"\nNow write a number: ";
std::cin>>y;
z = myFunc(x,y);
std::cout<<"\n the answer is:" << z;
system("pause");
return 0;
}

float myFunc(unsigned short int x, unsigned short int y)
{
 

}

---

I don't have a clue of what to put in my function. everytime i try it just ends up with some sort of a loop.
Don't laugh, i just started reading this book a couple of hours ago. And this recursive functions is hard for me to understand.

Ok. I tried some more. This is what i got.

Code:

---

#include <iostream>
#include <stdlib.h>
float sum;
int count = 1;
float myFunc(unsigned short int x, unsigned short int y);
int main()
{
unsigned short int x = 0;
unsigned short int y = 0;
float z;

std::cout<<"Write a exponent: ";
std::cin>>x;
std::cout<<"\nNow write the number: ";
std::cin>>y;
sum = y;
z = myFunc(x,y);
std::cout<<"\n the answer is:" << z;
system("pause");
}

float myFunc(unsigned short int x, unsigned short int y)
{
if(count==x)
return sum;
else{
count++;
sum = sum * y;
return(myFunc(x,y));
}
}

---

It works. But it just seams so , i dont know, uncorrect. I seams like i use a method that is not what the author of my book intended.
Any comments?

Yes, you want to avoid using global variables when possible. The method I came up with involves passing x as two of the parameters of "myFunc" , where x1^y. The second x2 would change when the function recurses...ok maybe that doesn't make much sense so:

Code:

---

float power(float x1,float x2,int y)
  {
    if (y>1)
        power(x1,(x2*x1),(y-1));
    else
      return x2;
  }

---

Code:

---

int power(int base, int exp)
{
    if (exp == 0)
        return 1;

    return (power(base, exp - 1) * base);
}

---

I knew there was a better way...:o

What are you guys talking about.

Code:

---

template<int x, unsigned int y>
struct power
{
  static const int val = x * power<x, y - 1>::val;
};

template<int x>
struct power<x, 0>
{
  static const int val = 1;
};

---

;)

Zach, that is only for compile time.

This should work,

Code:

---

#include <iostream>
#include <stdlib.h>

float myFunc(unsigned int, unsigned int);

int main()
{
      unsigned short int exponent = 0;
      unsigned short int number = 0;
      float z;

      std::cout<<"Write a exponent: ";
      std::cin>>exponent;

      std::cout<<"\nNow write a number: ";
      std::cin>>number;

      z = myFunc(exponent, number);
      std::cout<<"\nThe answer is : " << z << endl << endl;

      system("PAUSE");
      return 0;
}

float myFunc(unsigned int exp, unsigned int num)
{
      if (exp > 0)
        return (float) (num * myFunc( --exp, num) );

      return 1;
}

---

Why does the function return a float anyway?

Eibro's code is still the best.

Thanks for all the replies. I will analyze this carefully now.

" CornedBee: Why does the function return a float anyway?"

I just thought that would be the best way. Because this numbers usualy gets very big.

example: 5^11 = very high number.
And im not sure how high an int can go.
As I stated earlier in this thread, im a newbie, but thats what i think.

int can go up to 2 billion, unsigned int to 4 billion (on 32-bit systems anyway).

To be more specific, the highest possible value of int is
2^31 - 1
and of unsigned int
2^32 - 1

oh thanks. thats good to know

Quote:

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Originally posted by CornedBee
Zach, that is only for compile time.

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Yes, I know... It was really just a joke.