How do I store numbers that matches in an array? - c++

Question

I want to add the index of arrayOfNumbers that matched to numToMatch to an array. Not sure how to go about this. I'm new to C++. Any help would be appreciated ty.
int numToMatch[4] = {1,2,3,4};
int arrayOfNumbers[7] = {0, 1, 2, 3, 4, 5, 6};
int IndexThatMatched[4]; // Want to add to this Array.
int main()
{
for(int i = 0; i < 4; i++)
{
for(int j = 0; j < 7; j++)
{
if(numToMatch[i] == arrayOfNumbers[j])
{
cout << "Num " << numToMatch[i] << " ";
cout << "matches " << arrayOfNumbers[j];
cout << endl;
}
}
}
}

Answer 1

Added only two lines.
int numToMatch[4] = {1,2,3,4};
int arrayOfNumbers[7] = {0, 1, 2, 3, 4, 5, 6};
int IndexThatMatched[4]; // Want to add to this Array.
int main()
{
for(int i = 0; i < 4; i++)
{
IndexThatMatched[i] = -1;
for(int j = 0; j < 7; j++)
{
if(numToMatch[i] == arrayOfNumbers[j])
{
cout << "Num " << numToMatch[i] << " ";
cout << "matches " << arrayOfNumbers[j];
cout << endl;
IndexThatMatched[i] = j;
}
}
}
}
If there was no match for numToMatch[k] then IndexThatMatched[k] will be -1.
In your example IndexThatMatched will be: {1, 2, 3, 4}.
That's because numToMatch's elements are positioned in indices 1-4 of arrayOfNumbers.
Moreover, after that run, for any k in the safe range:
numToMatch[k] == arrayOfNumbers[IndexThatMatched[k]]

Answer 2

If you really want to learn C++ ditch the C-style arrays and start practising with containers. If you combine them with the functions in <algorithm> you can write something like this:
std::vector<int> MatchNums{1,2,3,4};
std::vector<int> NumsToMatch{0, 1, 2, 3, 4, 5, 6};
std::vector<int> MatchedNums;
for ( auto Number:NumsToMatch )
{
auto Match = std::find( MatchNums.begin(), MatchNums.end(), Number );
if ( Match != MatchNums.end() )
{
MatchedNums.push_back( *Match );
}
}
for ( auto i:MatchedNums )
{ //Print out the found numbers:
std::cout << i << std::endl;
}
There's a lot more ways of doing this by combining different algorithms and I encourage you to try and think of as many ways as you can and try them all out.