How to use compare function in sort()

I have seen compare function in sort to sort using the second element and all! But i am not understanding the syntax. Can anyone please provide the syntax to sort the pairs by the sum of the elements or product of the elements so that i will get the idea of the compare function

Thanks in advance!

Well the general syntax of the sort() function is
sort(start,end,overload function);
where the “overload function” is the one we provide to overload the original function of the c++.
As for sorting by sum or product just write a overload function as:

typedef pair<int,int> ii;
#define first f
#define s second
bool cmp(ii a,ii b)
 int as=a.f+a.s,bs=b.f+b.s;
    return as<bs;
  return a.f<b.f;

struct _pair
int first, second;

    /*in order to sort an array of _pair in increasing order based on the sum/product of the elements of _pair write a compare function like this.. The value returned (either 1 or 0) indicates whether the element passed as first argument is considered to go before the second.... */

    int compare(const _pair& x, const _pair& y)
    return (x.first+x.second) < (y.first+y.second); //modify it for sorting by product of elements

Suppose if i can use only qsort() where should i give compare as the argument in the function call? If C++ is blocked in a contest with only C/JAVA

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Please refer this link:

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