c++ passing pointers to a function - c++

Question

I am trying to create a console app in C++ that prompts the user to enter a floating point number and then takes that number and separates out the integer part and the fraction part.
Example output would be:-
Please enter a floating point number:
800.589
The integer part is 800 and the fraction part is .589
My solution is shown below:
#include <iostream>
#include <cmath>
using namespace std;
void spliceAnyNumber (double anyNumber)
{
double integerPart = 1;
double fractionPart = 1;
double *pIntegerPart = &integerPart;
double *pFractionPart = &fractionPart;
fractionPart = fmod(anyNumber,1);
integerPart = anyNumber - fractionPart;
cout << "The integer part is " << *pIntegerPart << " and the fraction part is " << *pFractionPart << "\n";
cout << endl;
cout << "The address of *pIntegerPart is " << &integerPart << "\n";
cout << endl;
cout << "The address of *pFractionPart is " << &fractionPart << "\n";
cout << endl;
}
int main()
{
cout << "Please enter a floating point number: ";
double anyNumber = 0;
cin >> anyNumber;
cout << endl;
spliceAnyNumber(anyNumber);
system("Pause");
return 0;
}
I wrote the program but I am also being asked to pass pointers to the function and manipulate the dereferenced values. I tried to do that below but I am getting a bunch of errors back from the compiler.
#include <iostream>
#include <cmath>
using namespace std;
void spliceAnyNumber (double *pAnyNumber)
{
double integerPart = 1;
double fractionPart = 1;
double *pIntegerPart = &integerPart;
double *pFractionPart = &fractionPart;
&fractionPart = fmod(&anyNumber,1);
&integerPart = &anyNumber - &fractionPart;
cout << "The integer part is " << *pIntegerPart << " and the fraction part is " << *pFractionPart << "\n"; *pFractionPart << "\n";
cout << endl;
cout << "The address of *pIntegerPart is " << &integerPart << "\n";
cout << endl;
cout << "The address of *pFractionPart is " << &fractionPart << "\n";
cout << endl;
}
int main()
{
cout << "Please enter a floating point number: ";
double *pAnyNumber = &anyNumber;
cin >> *pAnyNumber;
cout << endl;
spliceAnyNumber(*pAnyNumber);
system("Pause");
return 0;
}
Where am I going wrong with adding in pointers? Version 1 works but version 2 does not.

Answer 1

I've notated this inline.
#include <iostream>
#include <cmath>
using namespace std;
void spliceAnyNumber (double *pAnyNumber)
{
double integerPart = 1;
double fractionPart = 1;
double *pIntegerPart = &integerPart;
double *pFractionPart = &fractionPart;
&fractionPart = fmod(&anyNumber,1); // <- you should dereference pAnyNumber instead, and assign to fractionPart (i.e. "fractionPart = fmod(*pAnyNymber, 1);
&integerPart = &anyNumber - &fractionPart; // <- similar as above
cout << "The integer part is " << *pIntegerPart << " and the fraction part is " << *pFractionPart << "\n"; *pFractionPart << "\n";
cout << endl;
cout << "The address of *pIntegerPart is " << &integerPart << "\n";
cout << endl;
cout << "The address of *pFractionPart is " << &fractionPart << "\n";
cout << endl;
}
int main()
{
cout << "Please enter a floating point number: ";
double *pAnyNumber = &anyNumber; // <- you haven't declared an 'anyNumber' variable to take the address of
cin >> *pAnyNumber;
cout << endl;
spliceAnyNumber(*pAnyNumber);
system("Pause");
return 0;
}

Answer 2

The & operator takes the address of a variable, so typeof(&anyNumber) == double**. You want the * operator instead.
You should read double *pAnyNumber as "When I apply the * operator, I get a double". (You actually get an lvalue reference, but that doesn't roll off the tongue and will probably confuse you...)
Your main function is a mess; leave it the same as the original and change spliceAnyNumber(pAnyNumber); to spliceAnyNumber(&pAnyNumber);.

Answer 3

I assume when you wrote anyNumber you actually meant pAnyNumber. If you have a pointer
double* p;
You dereference by *p, not &p. The former gives you a double while the latter gives you a double**.

Answer 4

You have to declare anyNumber before you can dereference it:
double *pAnyNumber = &anyNumber; // references an undeclared variable
Just take the address when passing to the function. Before that, you can use normal variables - no need for pointers:
double anyNumber;
cin >> anyNumber;
cout << endl;
spliceAnyNumber(&anyNumber);
Additionally, you're using the wrong operator in your function. It should be like this:
*pFractionPart = fmod(*pAnyNumber,1);
*pIntegerPart = *pAnyNumber - fractionPart;
The other thing is invalid syntax: &variable = ... literally means "address of variable = ", which results in a double**.
So the only change you have to make is the function parameter, and accessing it. No need for all those pointers inside the function..