C18 RAM c-string – Withouth copying

The C18 compiler supports the number-to-ascii family of standard C functions in stdlib.h: itoa(), ltoa(), ultoa() et cetera.

Depending on which compiler / stdlib.h you have, the relevant function prototype would be:

extern char *   itoa(char * buf, int val, int base); // signed int
extern char *   utoa(char * buf, unsigned val, int base); // unsigned int

or

extern char *   itoa(char * buf, int val); // signed int
extern char *   utoa(char * buf, unsigned val); // unsigned int

If you were looking for a relatively robust built-in "standard" C way for converting your numbers to ASCII strings, these xtoa() functions would be the ones to use.

If on the other hand you are constrained to squeeze a few extra cycles or bytes of memory out of the final code, then several of the other answers to your question are the way to go.

It's because the following section of code will be trying to set start to 100,000 for numbers equal to or above 10,000 which is too big for an unsigned int which is a 16-bit and can only hold 0-65535:

while (start <= input)
    start *= 10;

Changing the definition to the following should fix it:

unsigned long start = 1;

Another alternative to make the code clearer is to include stdint.h so it may be defined as the following that will work across compilers:

#include <stdint.h>
uint32_t start = 1;