#include <iostream>
#include <cstring>
 
int atoi(const char*);
 
// Definitions of Required Functions 
int single_char_convert(char);
int pow(int,int);
int convert(const char*,int,int);
 
// DEFINITOINS END 
int main()
{
std::cout<<atoi("123")<<" DECIMAL \n";
std::cout<<atoi("0112")<< " Octal == 74\n";
std::cout<<atoi("0x1128")<<" HEXADECIMAL == 4392\n";
 
}
 
 
int atoi(const char *str)
{
	if (str[0]=='0'&&(std::tolower(str[1])=='x'))
	{
		return convert(str,16,2);	//Hexadecimal
	}
	else if(str[0]=='0')
	{
		return convert (str,8,1);	//Octal
	}
	else{
		return convert(str,10,0);	//Decimal
	} 
}
 
int convert(const char *str,int value,int start)
{
	int length=std::strlen(str)-1;
	int result=0;
	for(int x=start;x<=length;x++)
	{
		int y=length-x;
		char character=tolower(str[x]);
		int converted_char=single_char_convert(character);
		if(converted_char==-1)
		{
		std::cerr<<"\nInvalid Input,at "<< character <<" is an error\n";
		return -1;
		}
		result+=(converted_char*pow(value,y));			
	}
	return result;
}
 
 
int single_char_convert(char a)
{
	char index[]="0123456789abcdef";
	for(int count=0;count<16;count++)
	{
		if(index[count]==a)
		{
		return count;
		}
	}
	std::cerr<<"Error Invalid Character Input";
	return -1;
}
 
int pow(int number,int powerof)
{
 
	if (powerof==0)
	{
	return 1;
	}
	else if(powerof<0)
	{
	std::cerr<<"ERROR ERROR Wrong Power "<< powerof <<" which is less than 0";
	}
	else
	{
	return number*pow(number,--powerof);
	}
}