Program seems to skip 'if' statement - c++

Question

I'm attempting to create a program that will multiply 3 not equal values from vector 1 ('V1'), and write in vector 2 ('V2'). I'm using 3 'for' loops and an integer that counts vector 2's value's number. But program skips the 'if' statement.
#include <vector>
#include<fstream>
#include<iostream>
#include <algorithm>
using namespace std;
void earase(vector<int> V2, unsigned int z){
V2.erase(V2.begin() + z);
}
void main(){
unsigned int N;
unsigned int z = 0;
vector<int> V1;
vector<int> V2;
int input;
ifstream file1;
file1.open("input.txt");
file1 >> N;
for (unsigned int i = 0; i < N; i++){
file1 >> input;
V1.push_back(input);
}
file1.close();
for (unsigned int i = 0; i < V1.size(); i++){
for (unsigned int j = 0; j < V1.size(); j++){
for (unsigned int k = 0; k < V1.size(); k++){
V2.push_back(V1[i] * V1[j] * V1[k]);
if (i == j || i == k || j == k || (i == k ) && k==j)
{
void earase(vector<int> V2, unsigned int z);
}
z++;
}
}
}
sort(V2.begin(), V2.end());
ofstream file2;
file2.open("output.txt");
file2 << V2.back();
file2.close();
}
Here is the input.txt file
4
1 2 3 4
After finishing the program sorts the vector 2 and writes the last number in vector 2 in 'output.txt' but it writes values that will come only if multiply the same value from vector 1, 3 times.
I think the problem is in 'if' statement, and 'z' integer, is there any more efficient way to do this?

Answer 1

Non equal positions is trivial, no test required (assuming you want each combination only once):
for (unsigned int i = 0; i < V1.size(); i++){
for (unsigned int j = 0; j < i; j++){
for (unsigned int k = 0; k < j; k++){
V2.push_back(V1[i] * V1[j] * V1[k]); } } }
If for some reason, you wanted all each combination multiple times (as if you had gone through all N cubed possibilities skipping only duplicate positions) just go through the above simple way and push each multiple times.

Answer 2

The body of your if is actually something quite different than you expect:
if (i == j || i == k || j == k || (i == k ) && k==j)
{
void earase(vector<int> V2, unsigned int z); // <<<<<<<
}
You're not calling earase. Instead, you're declaring a function called earase. If you want to call the function, call it:
if (i == j || i == k || j == k || (i == k ) && k==j)
{
earase(V2, z);
}
By the way you could have easily checked that with some debugging output (like std::cout << "if entered"; after/before earase). However, keep in mind that this won't actually change V2.