Base conversion from any base to any base in C (up to 36)

Question

im looking for a base conversion function in c that could do conversions from bases 2 up to 36, including bases with characters A-Z.

For now i just found on the web functions that deal with base 2, ten and hex and a bit limited.

Answer 1

For this project, it would probably help to understand how bases work. In any case, let's walk through a process for how one might convert to, say, base twelve. This should be the simplest method to implement.

First up, we have our decimal number, since that's an easy place to start. Let's say, I dunno, 1452 is our number. We'll also need an array of characters for what each character is, since that'll be a lot easier than a straight ASCII conversion, where the number characters and letter characters are separated.

int dec=1452;
int toBase=12;
char outputs[36]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'}

Following that, we probably will only be OUTPUTTING the result in another base - it doesn't make sense to store it multiple ways, and makes your conversion process simpler by only converting from one base to any other given. We could store the result in a character array, but again, we already have the number stored - no point.

For this method I'm going to describe, we'll need a buffer variable to keep track of our number as we convert parts of it.

int buf=dec;

Next up, we'll start counting spaces back in the base we're going to, 12, and see what each space is worth. We'll continue until we pass our number, then backtrack one. We'll also need to save what space we're on for a for loop from that to the first space later.

int space=0;
while(Math.pow(toBase,space))<buf){
  space++;
}//Braces added for clarity
space--;

Now, this is the main calculation loop, where we'll output the result. Again, the original number is still stored in 'dec,' so we don't need to worry about loss of data or changing it at all.

int i;
for(i=space;i>=0;i--){//We have set up the for loop to check each space as we progress
  int modResult=buf%Math.pow(toBase,i);//Gets the number that goes in this space of the resulting base number
  buf-=modResult*Math.pow(toBase,i);//We have that, so take it out of the number
  printf("%c",outputs[modResult]);
}

Because of the way we're doing this, going from the top space to the bottom, modResult will never be higher than the highest number our base can go in. With this, your program will output to console the resulting number. Also, keep in mind that this only outputs the number - for the purposes of storage and calculation, it's much simpler to use the built-in functions that use base 10. Furthermore, be careful that your toBase variable never goes above 36.

As a further note, I numbered the digits (spaces), from right to left, starting at zero, because the far right space is 1, represented by your base to the zeroth power. Hope this helps.