Fixed-point arithmetic provides a way to handle floating point numbers using only simple integer data types. As an example, the value 3.141 could be represented as an integer with a value of 3141 - in this case the value has a fixed-precision of 3 decimal places.

#include <stdint.h>
 
int32_t strntofp(const char *s, char **endptr, size_t n, char dp)
{
        int32_t i = 0;
        char neg = 0, fp = 0;
 
        if(n <= 0) goto out;
 
        /* Test for a + or - sign */
        switch(*s)
        {
        case '-': neg = !neg;
        case '+': s++; n--;
        }
 
        /* Read in the number */
        while(*s && n && (!fp || dp))
        {
                char d = *s;
 
                if(d >= '0' && d <= '9')
                {
                        /* Add the digit */
                        i *= 10;
                        i += d - '0';
 
                        if(fp) dp--;
                }
                else if(dp > 0 && d == '.') fp = 1;
                else break;
 
                /* Next... */
                s++;
                n--;
        }
 
        while(dp > 0)
        {
                i *= 10;
                dp--;
        }
 
        /* Fix result if it's negative */
        if(neg) i = -i;
 
out:
        /* Set the end pointer if needed */
        if(endptr) *endptr = (char *) s;
 
        return(i);
}