Add modular_exponentiation

math/modular_exponentiation

@@ -0,0 +1,44 @@
+// Iterative C++ program for modular exponentiation.
+//The program calculates the value of an integer raised to an integer exponent under modulo an integer.
+#include <iostream> 
+
+
+// Iterative Function to calculate a raised to exponent b under modulo c in O(log b) 
+int power(int a, unsigned int b, int c) 
+{ 
+	int ans = 1;	    // Initialize the answer to be returned 
+
+	a = a % c;          // Update a if it is more than or 
+				        // equal to c 
+
+	if (a == 0) 
+	{
+	    return 0;       // In case a is divisible by c; 
+	}
+	
+	while (b > 0) 
+	{ 
+		// If b is odd, multiply a with answer 
+		if (b & 1) 
+		{
+			ans = (ans*a) % c; 
+		}
+		
+		// b must be even now 
+		b = b>>1;       // b = b/2 
+		a = (a*a) % c; 
+	}
+	
+	return ans; 
+} 
+
+// Main Function
+int main() 
+{ 
+	int num1 = 2; 
+	int num2 = 5; 
+	int m = 13; 
+	std::cout << "The value of "<<num1<<" raised to exponent "<<num2<<" under modulo "<<m<<" is " << power(num1, num2, m); 
+	return 0; 
+} 
+