Renamed Datastructures -> Data Structure

Following uniform naming convention in the repo

Data Structure/Stack Using Array.cpp

@@ -0,0 +1,80 @@
+#include<iostream>
+using namespace std;
+
+int *stack;
+int top=0, size;
+
+void push(int x)
+{
+	if(top==size)
+	{
+		cout<<"\nOverflow";
+	}
+	else
+	{
+		stack[top++]=x;
+	}
+}
+
+void pop()
+{
+	if (top==0)
+	{
+		cout<<"\nUnderflow";
+	}
+	else
+	{
+		cout<<"\n"<<stack[--top]<<" deleted";
+	}
+}
+
+void show()
+{
+	for (int i = 0; i < top; i++)
+	{
+		cout<<stack[i]<<"\n";
+	}
+}
+
+void topmost()
+{
+    cout << "\nTopmost element: "<<stack[top-1];
+}
+int main()
+{
+	cout<<"\nEnter Size of stack : ";
+	cin>>size;
+	stack = new int[size];
+	int ch, x;
+	do
+	{
+		cout<<"\n1. Push";
+		cout<<"\n2. Pop";
+		cout<<"\n3. Print";
+        cout<<"\n4. Print topmost element:";
+        cout<<"\nEnter Your Choice : ";
+		cin>>ch;
+		if (ch==1)
+		{
+			cout<<"\nInsert : ";
+			cin>>x;
+			push(x);
+		}
+		else if (ch==2)
+		{
+			pop();
+		}
+		else if (ch==3)
+		{
+			show();
+		}
+        else if(ch==4)
+        {
+            topmost();
+        }
+	}
+	while(ch!=0);
+
+	return 0;
+}
+