What are the run-time problems here?

#include <stdio.h> add(double p1, p2) { return p1 + p2; } double add2(double p1, p2) { return p1 + p2; } main() { double a = 13.4, b = 67.99, c; c = add(a,b); printf("Add - %f \n",c); c = add2(a,b); printf("Add2 - %f \n",c); }