c++ - Returning in double functions -

double interpolation(int input, vector<int>&a, vector<double>&b) {     for(int i=0;i<a.size();++i)     {         if(input==a.at(i))             return b.at(i);     }      for(int i=0;i<a.size()-1;++i)     {         if(input>a.at(i)&&input<a.at(i+1))         {             int low=i;             int high=i+1;             double m= b.at(low);             int n= input-a.at(low);              int p= a.at(high) - a.at(low);             double q= b.at(high) - b.at(low);              double fp = (m+n) / (p*q);             return fp;         }     }         } 

i keep getting warning: control reaches end of non-void function [-wreturn-type] } message.

i know has way i'm returning value function. purpose of function calculate f(b) = f(a) + (b - a)/(c - a)(f(c) - f(a)). it's hard explaining equation is, yeah return trick think.

you getting warning because code not return value when size of 'a' vector zero. should return 0 in event, unless error code more appropriate.