start point power and factorial operation

src/main/c/Calculator/calculator.c

@@ -17,6 +17,8 @@ double cosine(double angle);
 double tangent(double angle);
 double permutation(int n, int r);
 double combination(int n, int r);
+double factorial(double num);
+double power(double base, double exponent);
 
 int main() {
     double choice, num1, num2, result, angle;
@@ -120,6 +122,7 @@ int main() {
                 result = combination(n, r);
                 printf("Combination of %d and %d: %lf\n", n, r, result);
                 break;
+
                 case :
                 printf("Exiting...\n");
                 break;