You haven;t fully specified the requirements for your function, so I can only guess.
You have a number of inputs that you haven't supplied. Presumably those would be arguments to your function. You don't do anything with total, so presumably, that would be the return value from your function.
1 2 3 4
double functioname (double pods, double jet, double proton, double oxy)
{ // what you have
return total;
}
Line 13: pods + "$ " isn't going to do what you're expecting.