Convert string in pentadecimal to int

[Anonymouse]

ok... You may have seen my other thread about the reverse. (jdd, thanks for the help, and sorry I didn't reply to that. It helped a lot though.)
If not, look at http://www.cplusplus.com/forum/general/8950/

Anyway, now for the question - How would you go about converting a string containing a number in pentadecimal base into an int? This again needs to be a standard function or an explanation for how to write your own.

Thanks in advance,
Anonymouse

[Disch]

The idea is to isolate each digit and convert one digit at a time.

For example... break down a base-10 number:

"167" can be broken down to:


7*(10^0) = 7*1 = 7
6*(10^1) = 6*10 = + 60
1*(10^2) = 1*100 = + 100
-----
167 <-- base 10 result


This logic applies to numbers of any base N... just instead of 10, you use N. If, say, "167" was in base 8 and not base 10:


7*(8^0) = 7*1 = 7
6*(8^1) = 6*8 = + 48
1*(8^2) = 1*64 = + 64
-----
119 <-- base 10 result


The same logic can be applied for base 15. Just treat 'A'-'E' as 10-14, and multiply by (15^x)

In code -- this process can be even simpler. Simply keep a running sum of each digit, and multiply by the base between additions:

result = 0;
while( __digits_remaining__ )
{
  result *= base;
  result += next_digit;
}

with that same base 10 example -- say we have 167:


"167"

sum = 0 next digit="1"
sum = (0*10)+1 = 1 next digit="6"
sum = (1*10)+6 = 16 next digit="7"
sum = (16*10)+7 = 167


This works with other bases as well. Same example, base 8:


sum = 0 next digit="1"
sum = (0*8)+1 = 1 next digit="6"
sum = (1*8)+6 = 14 next digit="7"
sum = (14*8)+7 = 119