Regarding the operations on Stack you can see here

Since Stack is a list of links to form front to back, so we can not direct public 2 Stack. Suppose need community at Stack Stack S2 S1, we use 1 Stack Stemp to store intermediate values ​​of S2 and then only turn putting values ​​into S1 Stemp.
If community 2 Stack sang 1 The new stack is to transfer all 2 Stack Stack to mediate before switching to the necessary public Stack. Stack plus many similar actions.

#include <iostream>
#include <stack>

using namespace std;

int main(){
	stack <int> S1;
	stack <int> S2;
	stack <int> Stemp;
	
	// create 2 Stack
	for (int i = 0; i < 5; i++)
		S1.push(i);		// S1 : 0 1 2 3 4 
	for (int i = 5; i < 10; i++)
		S2.push(i);		// S2 : 5 6 7 8 9
	
	// move S2 to Stemp;
	while (!S2.empty()){
		int x = S2.top();
		S2.pop();
		Stemp.push(x);		// Stemp : 9 8 7 6 5
	}
	
	// move Stemp to S1
	while(!Stemp.empty()){
		int x = Stemp.top();
		Stemp.pop();
		S1.push(x);		// S1 : 0 1 2 3 4 5 6 7 8 9
	}
	
	// show S1
	
	while (!S1.empty()){
		int x = S1.top();
		S1.pop();
		cout << x << " ";
	}
	
	return 0;
}