Example

int main(int argc, char* argv[])
{
double b1 = -12.0;
double result = Math.abs(b1);
return 0;
}

Solution
Use fabs function to prevent loss of precision.

int main(int argc, char* argv[])
{
double b1 = -12.0;
double result = Math.fabs(b1);
return 0;
}