how to translate this if statement?into the common form

can someone please translate this if statement into the common form? I cant understand what it means..

//str[i++] = (rem > 9) ? (rem - 10) + 'a' : rem + '0';

taken from this code:

while (num != 0)
    {
        int rem = num % base;
        str[i++] = (rem > 9)? (rem-10) + 'a' : rem + '0';
        num = num/base;
    }

thanks