double - 1 divided by very large number return 0, C -

i decided post question because i'm not sure why i'm getting result. researched in site , others finding no solution. sorry if i'm violating websites rules remember, i'm new. code of function written in c returning unexpected result:

double gauss (double average, double variance, int data)     {     double model,power;     power = ((((data-average)*(data-average))/(2*variance))*(1));     model = (pow(e,(int)power));     return 1.0/model;     } 

i don't know if should post rest of code if want to, wanted keep post short. issue occuring 1.0/model because model big number.

c doubles have limited precision, if divide 1.0 large double, precision error net 0 (effectively, actual answer close 0 precision error round zero).

you try use long double more precision, think better off using arbitrary precision library gmp.