Find numeric substring with integers only - c++

Question

The Question :
If the sequence of digits in X forms a substring of the sequence of digits in Y, it outputs "X is a substring of Y"; otherwise, if the sequence of digits in X forms a subsequence of the sequence of digits in Y, then it outputs "X is a subsequence of Y"; otherwise, it outputs "X is neither substring nor subsequence of Y".
DO NOT use arrays or strings in this program
The output should be as follows
Enter Y : 239847239
Enter X : 847
X is substring of Y
Enter Y : 239847239
Enter X : 3923
X is subsequence of Y
Enter Y : 239847239
Enter X : 489
X is neither substring nor subsequence of Y
And below is what I got so far... (haven't coded anything for subsequence as i was clueless)
I know my coding is very unefficient and is only suitble to use for the above model output. Any improvements or comments how to fix this would be greatly appreciated.
#include <cmath>
#include <iostream>
using namespace std;
int main() {
cout << "Enter Y: " ;
int Y;
cin >> Y;
cout << "Enter X: ";
int X;
cin >> X;
if (Y >= X){ // Below are all the possibilities of substrings up to 9 decimal places.
if( X == (Y % 10)) cout << "X is substring of Y";
else if (X == (Y % 100)) cout << "X is substring of Y";
else if (X == (Y % 1000)) cout << "X is substring of Y";
else if (X == (Y % 10000)) cout << "X is substring of Y";
else if (X == (Y % 100000)) cout << "X is substring of Y";
else if (X == (Y % 1000000)) cout << "X is substring of Y";
else if (X == (Y % 10000000)) cout << "X is substring of Y";
else if (X == (Y % 100000000)) cout << "X is substring of Y";
else if (X == (Y % 1000000000)) cout << "X is substring of Y";
else cout << "X is neither substring nor subsequence of Y";
}
else cout << "neither subsequence nor subset"; // prints out when Y is less than X.
return 0;
}

Answer 1

This what i got by far:
Substring
bool substring(long x, long y){
double auxX = x;
int power = 0;
while (auxX >= 1){
auxX /= 10;
++power;
}
int mask = pow(10, power);
int reminder;
while (y > 0){
reminder = y % mask;
if (reminder == x){
return true;
}
y /= 10;
}
return false;
}
Subsequence
bool subsequence(long x, long y){
int lastX;
int lastY;
while (y > 0){
lastX = x % 10;
lastY = y % 10;
if (lastX == lastY){
x /= 10;
if (x <= 0){
return true;
}
}
y /= 10;
}
return false;
}
Main
int main()
{
long x = 21;
long y = 469721481;
if (substring(x, y)){
cout << x << " is substring of " << y << std::endl;
}
else if (subsequence(x, y)){
cout << x << " is subsequence of " << y << std::endl;
}
else{
cout << x << " is neither substring nor subsquence of " << y << std::endl;
}
return 0;
}
I've tested some cases and it seems to work fine, but you should test with edge cases (multiple repetitions of the same pattern, one digit numbers, zeros, etc) and retouch this snippet