Variable initation problem

[fizanimtiaz93]

So I have a template, part of a larger code, that is designed to calculate the number of multiplications it took to reach a certain number. The problem is, whenever I execute the program, mults is always printing out a strange number, perhaps its actual address. Can someone please shed light on my problem?

template <class T>
T power3(T x, unsigned int n, unsigned int& mults)
{
    if (n == 0) return 1;
    if (n == 1) return x;
    if (n == 2){
	mults++;
	return x * x;
    }
    if (n%2 == 0){
	mults++;
	return power3((power3(x,(n/2),mults)),2,mults);
    }
    else if(n%2 != 0){
	mults++;
	return x * power3((power3(x,((n-1)/2),mults)),2,mults);
    }

   return 0;
}

[MikeyBoy]

Well, what are you initialising it to in the calling code? Without seeing the code that initialises it, and maybe the code that prints it out, there's not a lot we can tell.

[giblit]

The problem is probably due to x or mults being uninitalized as mikeyboy mentioned or a faulty return from power3.

[fizanimtiaz93]

Oh. Sorry, here is the whole code:

#include <iostream>
using namespace std;

template <class T>
T power1(T x, unsigned int n, unsigned int& mults);

template <class T>
T power2(T x, unsigned int n, unsigned int& mults);

template <class T>
T power3(T x, unsigned int n, unsigned int& mults);

template <class T>
void printReport(T base, unsigned int pow,
                 T result1, T result2, T result3,
                 unsigned int mults1, unsigned int mults2,
                 unsigned int mults3);
int main()
{
   unsigned int mults1, mults2, mults3;
   cout << "Test for integer base:\n";
   for (unsigned int pow = 0; pow <= 32; pow++) {
      unsigned int base = 2;
      unsigned int result1 = power1(base, pow, mults1);
      unsigned int result2 = power2(base, pow, mults2);
      unsigned int result3 = power3(base, pow, mults3);
      printReport(base, pow, result1, result2, result3,
                  mults1, mults2, mults3);
   }
   cout << "\nTest for floating-point base:\n";
   for (unsigned int pow = 0; pow <= 64; pow++) {
      double base = 0.5;
      double result1 = power1(base, pow, mults1);
      double result2 = power2(base, pow, mults2);
      double result3 = power3(base, pow, mults3);
      printReport(base, pow, result1, result2, result3,
                  mults1, mults2, mults3);
   }
}
template <class T>
T power1(T x, unsigned int n, unsigned int& mults)
{
    mults = 0;
    unsigned int temp;
    if (n == 0) return 1;
    if (n == 1) return x;
    else {
        for (temp = x; n > 1; n--){
            temp *= x;
            mults++;
        }
        return temp;
    }
    return 1;
}

template <class T>
T power2(T x, unsigned int n, unsigned int& mults)
{
    if (n == 0) return 1;
    if (n == 1) return x;
    else if (n > 1){
        mults++;
        return x * power2(x, n - 1, mults);
    }
    return 0;
}
template <class T>
T power3(T x, unsigned int n, unsigned int& mults)
{
    if (n == 0) return 1;
    if (n == 1) return x;
    if (n == 2){
        mults++;
        return x * x;
    }
    if (n%2 == 0){
        mults++;
        return power3((power3(x,(n/2),mults)),2,mults);
    }
    else if(n%2 != 0){
        mults++;
        return x * power3((power3(x,((n-1)/2),mults)),2,mults);
    }

   return 0;
}
template <class T>
void printReport(T base, unsigned int pow,
                 T result1, T result2, T result3,
                 unsigned int mults1, unsigned int mults2,
                 unsigned int mults3)
{
   cout << base << "^" << pow << " = ";
   if (result1 == result2 && result2 == result3)
      cout << result1 << ": ";
   else
      cout << "(" << result1 << ", " << result2 << ", " << result3
           << ") [ERROR!]: ";
   cout << "mults1 = " << mults1 << ", mults2 = " << mults2
        << ", mults3 = " << mults3 << endl;
}

[MikeyBoy]

So, yes, the problem is exactly as I guessed. You're not initialising mults3, so it's in an undefined state when you pass it into power3().

[fizanimtiaz93]

And I'm supposed to initialize it outside of the function itself, yes? Because setting it to 0 inside the function would set it back to 0 everytime the program recursively executed.

[MikeyBoy]

Yeah, that's right. "Initialisation" means giving a variable an initial value (usually at the time it's created). Which means that, by definition, it's a one-time action :)

In C++, if no value has been assigned to a variable (by initialisation, or by subsequent assignment) then its value is undefined. You should always initialise your variables, so that your program is always in a known, well-defined state.

[fizanimtiaz93]

So am I supposed to initialize it once for all the functions or a separate one for each?

[MikeyBoy]

Well, that's up to you. Do you want to store the values passed pack from the three different function calls separately? Or are you happy to overwrite each value with the result of the next call. What behaviour do you want your program to have?

[fizanimtiaz93]

I want this program to store each value separately, as it is going to print each out separately as well. What I did was declare two global variables and set their values to 0, made mults= each of the two variables in their respective functions.

[fizanimtiaz93]

Here are my changes to it:

using namespace std;
...
int j = 0;

int main(){
...
}
...
template <class T>
T power3(T x, unsigned int n, unsigned int& mults)
{
    mults = j;
    if (n == 0) return 1;
    if (n == 1) return x;
    if (n == 2){
        j++;
        return x * x;
    }
    if (n%2 == 0){
        j++;
        return power3((power3(x,(n/2),mults)),2,mults);
    }
    else if(n%2 != 0){
        j++;
        return x * power3((power3(x,((n-1)/2),mults)),2,mults);
    }
   return 0;
}