number-system-converter.cpp

#include <iostream>
#include <string.h>
#include <cmath>

int getInt(const char sym)
{
    switch(sym)
    {
        case '0': return 0;
        case '1': return 1;
        case '2': return 2;
        case '3': return 3;
        case '4': return 4;
        case '5': return 5;
        case '6': return 6;
        case '7': return 7;
        case '8': return 8;
        case '9': return 9;
        case 'a': case 'A': return 10;
        case 'b': case 'B': return 11;
        case 'c': case 'C': return 12;
        case 'd': case 'D': return 13;
        case 'e': case 'E': return 14;
        case 'f': case 'F': return 15;
        default: return -1;
    }
}

char getChar(const int num)
{
    switch(num)
    {
        case 0: return '0';
        case 1: return '1';
        case 2: return '2';
        case 3: return '3';
        case 4: return '4';
        case 5: return '5';
        case 6: return '6';
        case 7: return '7';
        case 8: return '8';
        case 9: return '9';
        case 10: return 'a';
        case 11: return 'b';
        case 12: return 'c';
        case 13: return 'd';
        case 14: return 'e';
        case 15: return 'f';
        default: return NULL;
    }
}

int getDecimal(const char *from, const int base)
{
    int temp, num = 0;
    bool isHex = (base > 10 && base <= 16);
    
    for(size_t i = 0, len = strlen(from); i < len; i++)
    {
        temp = getInt(from[i]);
        if(temp == -1 || (!isHex && temp > 9)){
            return -1;
        }
        num += temp * pow((double) base, len - i - 1);
    }
    
    return num;
}

const char *convert(int num, int base)
{
    int prev, temp = num, size = 0;
    while(temp != 0)
    {
        size++;
        temp /= base;
    }
    char *res = new char [size];
    for(int i = size - 1; i >= 0; i--)
    {
        prev = num;
        num /= base;
        res[i] = getChar(prev - num*base);
    }
    return res;
}