Question

Can someone please tell why I am unable to compile the following program:

#include<iostream>
#include<string>
#include<cmath>
#include<iostream>
#include<cfloat>
#define MOD 10000009

using namespace std;

double distance(pair<int,int> p1,pair<int,int> p2)
{
    double dist;
    dist = sqrt( (p1.first-p2.first)*(p1.first-p2.first) + (p1.second-p2.second)*(p1.second-p2.second) );
    return(dist);
}

int main()
{
        int N,i,j;
        cin >> N;
        pair<int,int> pi[N];
        for(i=0;i<N;i++)
        {
            cin >> pi[i].first >> pi[i].second;
        }

        for(i=0;i<N;i++)
        {
            cout << pi[i].first << " "<< pi[i].second << endl;
        }

        distance(pi[0],pi[1]); // This line is giving error

    return 0;
}

Answer 1

distance is defined by the standard library, which you already using‘ed into the global namespace, so it’s trying to use that one rather than the one you wrote (and expected).

Call your function something else to avoid the name clash.

Also just as style notes, in C++ code #define can usually be replaced with const or inline functions to provide much greater type safety, and I like to write using std::cout, etc for each item I need rather than using namespace std.