base conversion algo

This is a discussion on base conversion algo within the C++ Programming forums, part of the General Programming Boards category; i have got working the algo of converting decimal number to any other base. what will be the algo for ...

  1. #1
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    base conversion algo

    i have got working the algo of converting decimal number to any other base. what will be the algo for other way around?

  2. #2
    zen
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    You should be able to use the same principles. You could probably use one function/algorithm to do both. Something like -

    Code:
    #include <iostream> 
    #include <cmath>
    using namespace std; 
    
    int changebase(int num,int sourcebase,int destbase)
    {
    	int power=0;
    	int result=0;
    	while(num)
    	{
    		result += num%destbase*pow(sourcebase,power++);
    		num/=destbase;
    	}
    	return result;
    }	                                                                                                                                  
    
    int main() 
    { 
    	cout << changebase(10111,2,10);
    	return 0; 
    }
    This is limited to properly converting bases below 10 and the amount of digits it can handle (which could be a problem using the lower bases).
    zen

  3. #3
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    Join Date
    Dec 2001
    Posts
    194
    This code will allow you to convert between almost all bases
    It uses 0-9 as digits then a-z so in theory it will work for up to base 36.
    Hex aka base 16 uses 0-9,a-f
    so base 17 will use 0-9,a-g
    and base 18 will use 0-9,a-h
    I haven't tested all those, but for base 2,8,10 and 16 it should do just fine.
    It takes string as input so lenght is not an issue
    If anyone sees a way i could optomize the conversion lemme know
    Code:
    string ConvertBase(string number,int currentBase, int targetBase)
    {
    	string temp = "";
    	string answer;
    	char curr;
    	int value;
    	long int total=0;
    	for( int i=number.length()-1 ; i>= 0 ; i--)
    	{
    		curr = number[i];
    		if( isdigit(curr) )
    		{
    			value = curr - '0';
    		}
    		else if( isalpha(curr) )
    		{
    			curr = tolower(curr);
    			value = curr - 'a' + 10;
    		}
    		else
    		{
    			cout << "Error in input";
    			return temp;
    		}
    		total += value * pow(currentBase,number.length()-i-1);
    	}
    
    //	cout << total << endl;
    
    	// we now have the decimal value stored in total. time to convert it to the other base.
    
    	int power = 0;
    	
    	while(total)
    	{
    		value = total % targetBase;
    		total /= targetBase;
    		if( value < 10 )
    		{
    			temp += value + '0';
    		}
    		else
    		{
    			temp += value - 10 + 'a';
    		}
    	}
    	for( i=1 ; i<=temp.length() ; i++)
    	{
    		answer += temp[temp.length() - i];
    	}
    	return answer;
    }

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