Add monotonic stack demo with correct output order

basic dsa/MonotonicStackC++.cpp

@@ -0,0 +1,45 @@
+#include <bits/stdc++.h>
+using namespace std;
+//Function to demonstrate monotonic decreasing stack
+void decreasingMonotonicStack(vector<int> inputs){
+
+vector<int> stack;
+    for(int p:inputs){
+
+while(!stack.empty()  && stack.back()<=p){
+    stack.pop_back();
+}
+stack.push(p);
+
+    }
+    for (int val : stack) {
+    cout << val << " ";
+}
+    cout<<endl;
+}
+// Function to demonstarte monotonic increasing stack
+void increasingMonotonicStack(vector<int> inputs){
+
+vector<int> stack;
+    for(int p:inputs){
+
+while(!stack.empty()  && stack.back()>=p){
+    stack.pop_back();
+}
+stack.push(p);
+
+    }
+
+    for (int val : stack) {
+    cout << val << " ";
+}
+    cout<<endl;
+}
+int main(){
+vector<int> inputs={3,4,5,6,7,4,5,3};
+decreasingMonotonicStack(inputs);
+increasingMonotonicStack(inputs);
+
+
+
+}