splitting double into array in c

Question

I'd like the following code to work:

double num = 31415; /* num will never have a decimal part */
/* ... code here so that we can now say*/
printf("%d", num_array[0] == 3 && num_array[1] == 1 && num_array[4] == 5); //1

I realize it's trivial to do this with ints (just int i=0; while( num>0 ) numarr[size-++i]=num%10, num/=10; where size is predetermined to be the number of digits in the number) but that obviously won't work for floats/doubles because you can't mod one floats.

And yes, I need to use floats/doubles, despite not using the floating point section (it's an exercise).

And I have figured out how to determine the number of digits in a double, using a floor().

/* n > 0, n=floor(n) */
int numdigits(double n){
    int i = 0;
    while( n >0 ) n=floor(n/10), i++;
    return i;
}

Answer 1

Look up fmod. The number of digits will probably be easier to compute using log10.

Answer 2

It's probably easiest to just convert it to a string:

char* str = malloc(num_digits+1);
snprintf(str, num_digits+1, "%f", num);

Indexing into str will give you each digit as an ASCII value, so you'll need to subtract '0' to get the actual numeric value:

str[0] - '0' == 3;
str[1] - '0' == 1;
str[2] - '0' == 4;
...

Answer 3

Apart from fmod(), you could also cast to a int64_t or long long int, and use % as before. If the range is less than 10 digits, you could use a int32_t.