#include "stdafx.h"
#include <iostream.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

//Declarations:
//Takes a decimal number, converts it to base and stores the result in szString. Returns 1 on success or 0 on failure
int DecToBase(int,long,char*);
//Takes a number in any base and converts it to decimal.
//Number is a pointer to a string containing the value to convert (a string to allow for A-Z).
//Base is the base that number is in (e.g.16, if it is Hex)
int BaseToDec(char*,int);
//Returns position of a character in a string
int GetIndex(char *,char);

//Symbols used to display a number correctly
//Numbers over base 10 use letters to represent values over and equal to 10
//You should be able to increase the max no. of bases by adding other symbols
//Remember a string needs 1 extra space for null character
char symbols[37] = "0123456789ABCDEFGHIJKLMNoPQRSTUVWXYZ";
const int MAX_BASE = 36; //Highest base allowed (make sure there are enough symbols first!)
//

int main(int argc, char* argv[])
{
    char number[256] = "";
    cout << "Base conversion functions. Written by Matt Squire\n\n";
    //DecToBase samples
    cout << "Examples...\n\n";
    DecToBase(2,10,number);
    cout << "10dec to binary (base 2): " << number << endl;
    DecToBase(8,25,number);
    cout << "25dec to octal (base 8): " << number << endl;
    DecToBase(3,49,number);    
    cout << "240dec to base 36 (hexatridecimal?): " << number << endl;
    DecToBase(16,28,number);
    cout << "28dec to hexadecimal (base 16): " << number << endl;
    //I don't know why I wasted time working this one out... but 998453 spells LEET in base 36
    DecToBase(36,998453,number);
    cout << "998453dec to base 36: " << number << endl << endl;
    //BaseToDec samples
    cout << "4C9hex to decimal: " << BaseToDec("4C9",16) << endl;
    cout << "1760octal to decimal: " << BaseToDec("1760",8) << endl;
    cout << "1101011101bin to decimal: " << BaseToDec("1101011101",2) << endl << endl;
    //User input sample
    int iInput = 0,iBase = 2, iSrcBase = 10;
    cout << "Try another conversion...\nEnter a number in any base between 2 and 36 (must be integer): ";
    cin >> number;
    cout << "Enter a base to convert from: ";
    cin >> iSrcBase;
    cout << "Enter a base between 2 and 36 to convert to: ";
    cin >> iBase;
    //If the source base is not 10, convert it to 10 first
    if(iSrcBase!=10)
        iInput = BaseToDec(number,iSrcBase);
    else
        iInput = atoi(number);

    //If source base is not 10, and the destination base is, it is not nessecery to run DecToBase as the number
    //Has already been found in base 10
    if(iSrcBase!=10&&iBase==10)
    {
        cout << number << " in base " << iSrcBase << " = " << iInput << " in base " << iBase << endl << endl;
    }
    else
    {
        if(DecToBase(iBase,iInput,number))
            cout << iInput << " in base " << iSrcBase << " = " << number << " in base " << iBase << endl << endl;
        else
            cout << "Error: Base was out of bounds... (must be between 2 and 36)\n\n";
    }
    return 0;
}

int DecToBase(int base, long iDec, char* szString)
{
    //Check base is between 2 and 36
    if(base<2||base>MAX_BASE)
        return 0; //Failed
    //If input is 0, output is 0
    if(iDec==0){
        strcpy(szString,"0");
        return 1;
    }
    
    int count = 0;
    char chResult[256] = "";
    char* pChResult = chResult;
    while(iDec > 0 && count++<256)
    {
        *pChResult = symbols[iDec % base];
        pChResult++;
        iDec = iDec/base;    //iDec = itself divided by base
    }
    strcpy(chResult,_strrev(chResult));    
    strcpy(szString,chResult);

    return 1;
}

int BaseToDec(char* number, int base)
{
    if(base<2||base>MAX_BASE)
        return 0; //Failed

    int NumLength = strlen(number);
    int PlaceValue, total = 0;
    //Work out the place value of the first digit (base^length-1)
    PlaceValue = (int)pow(base,NumLength-1);
    
    //For each digit, multiply by its place value and add to total
    for(int i=0;i<NumLength;i++)
    {
        total += GetIndex(symbols,*number)*PlaceValue;
        number++;
        PlaceValue /= base; //Next digit's place value (previous/base)
    }
    return total;
}

//Finds the index of a particular character (if it exists) in an array. Returns last character on failure
//Used by BaseToDec to find face values
int GetIndex(char * pString, char search)
{
    int index = 0;
    while(*pString != (char)0) //Loop will finish at null character if no match is found
    {
        if(*pString==search)
            break;
        pString++;
        index++;
    }
    return index;
}

hex        dec
0            0
1            1
2            2
...
9            9
A            10
B            11
...
F            15