Added Fast Exponent using cpp

Author: AishwaryaGund

fastExponent.cpp

@@ -0,0 +1,31 @@
+#include <iostream>
+using namespace std;
+
+//Fast Exponentitation
+int fastExpo(int a, int n)
+{
+    int ans = 1;
+
+    while (n > 0)
+    {
+        int last_bit = (n & 1);
+        if (last_bit)
+        {
+            ans = ans * a;
+        }
+        a = a * a;
+        n = n >> 1;
+    }
+    return ans;
+}
+
+int main()
+{
+
+    int a, n;
+    cin >> a >> n;
+
+    cout << fastExpo(a, n) << endl;
+
+    return 0;
+}