Converting decimal to hex

I've been writing a program that will convert a decimal input to an octal or hex number. Basically I just need some help with the decimal to hex conversion. I searched the board for a while, but couldnt find anything...(I'm new to C++, so it might be that i just dont understand it.) Here's my code so far, thanks for any help!

Code:

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
enum ConverstionType {NONE,DECIMAL,HEX,OCTAL};
int number = 0;// a global variable visible throughout the file
int test = NONE;

// this function converts a char to upper case 
// and display it if not a digit representation;
void asciiToInt(char aChar){
	int digitValue = 0;
	switch(::test) {
		case OCTAL: {
					 digitValue = aChar - '0';
					::number *= 8;
					::number += digitValue;
					break;
		}
		case DECIMAL:
					{
					 digitValue = aChar - '0';
					::number *= 10;
					::number += digitValue;
					break;
					 }
		case HEX:
				{if (aChar >= 'a' && aChar <= 'f')
					digitValue = aChar - 'a' + 10;
				else
				digitValue = aChar - '0';
				::number *= 16;
				::number += digitValue;
				break;
				 }

		default: {
			cout << "error in conversion" << endl;
			::number = 0;
		}
	}
}

int main(){
string word;
cout << "enter a number:";
getline(cin,word);
	if(word[0] == '0')
		::test = OCTAL;
	else if(word[1] == 'x')
		::test = HEX;
	else
		::test = DECIMAL;
cout << word << endl;

// apply the function showChar to each character in the string
for_each(word.begin(),word.end(),asciiToInt);
cout << "converted number is " << number << endl;
return 0;
}

How about..

long number;
std::cout << "Please enter a number: ";
std::cin >> number;

std::cout << "\nIn hex: " << std::hex << number;
std::cout << "\nIn oct: " << std::oct << number;
std::cout << "\nIn dec << std::dec << number;

Thanks a lot! Thats a whole lot easier. I just dont know if my professor will take it. Know of a way to do it with the code that i started with??

Well, you're going to need a carry value from time to time when converting from a higher to lower base... or if you're converting from lower to higher base you'll need a borrow. You could search planet-source-code.com for examples of converting between hexadecimal/decimal/octal

Thanks for the help. There's a lot of good stuff on there too. Can someone tell me how to use a carry/borrow value? Like I said, I'm really new to this.

What do you mean by "carry and borrow"

Thats the problem...I dont really know. Refer to Eibro's post.

Originally posted by Mister C
What do you mean by "carry and borrow"

Nevermind, I guess I didn't look at his code closely enough.

>>Know of a way to do it with the code that i started with??
Yes, I also know of a better way. Here's a function that does what you want :-)

Code:

#include <algorithm>
#include <iostream>
#include <string>

using namespace std;

string hex_value(int decimal)
{
  static const string hex_digits("0123456789ABCDEF");

  string hex;
  int scratch = decimal;

  while (scratch != 0)
  {
    hex += hex_digits[scratch % 16];
    scratch /= 16;
  }

  reverse(hex.begin(), hex.end());

  return hex;
}

int main()
{
  cout<< hex_value(27) <<endl;
}

Thanks for everyone's help. I finally got it working using the form my professor wants. If anybody's interested, here's my final code. Thanks again.

Code:

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
enum ConverstionType {NONE,DECIMAL,HEX,OCTAL};
int number = 0;// a global variable visible throughout the file
int test = NONE;

// this function converts a char to upper case 
// and display it if not a digit representation;
void asciiToInt(char aChar){
	int digitValue = 0;
	switch(::test) {
		case OCTAL: {
					 digitValue = aChar - '0';
					::number *= 8;
					::number += digitValue;
					break;
		}
		case DECIMAL:
					{
					 digitValue = aChar - '0';
					::number *= 10;
					::number += digitValue;
					break;
					 }
		case HEX:
				{if (aChar >= 'a' && aChar <= 'f')
					digitValue = aChar - 'a' + 10;
					else if (aChar == 'x')
					digitValue = 0;
				else
				digitValue = aChar - '0';
				::number *= 16;
				::number += digitValue;
				break;
				 }

		default: {
			cout << "error in conversion" << endl;
			::number = 0;
		}
	}
}

int main(){
string word;
cout << "Enter a number to convert to decimal form:" << endl;
cout << "Octal numbers should be preceded by a 0." << endl;
cout << "Hexadecimal numbers should be preceded by an x." << endl;

getline(cin,word);
	if(word[0] == '0')
		::test = OCTAL;
	else if(word[0] == 'x')
		::test = HEX;
	else
		::test = DECIMAL;
cout << word << endl;
// apply the function showChar to each character in the string
for_each(word.begin(),word.end(),asciiToInt);
cout << "The Converted number is " << number << endl;
cout << " " << endl;

return 0;
}