Adding algorithm to check if number is prime or not. (TheAlgorithms#834)

* Optimized algorithm to check if number is prime or not.

* logic to check if given number is prime or not.

* logic to check if given number is prime or not.

* logic to check if given number is prime or not.

* logic to check if given number is prime or not.

* Included appropriate comments as per standards.

* variable name renamed to num

* added @file and @brief in comment. Also added template and variable name changed from is_prime to result

* added @file and @brief in comment. Also added template and variable name changed from is_prime to result

* added template parameter T type in loop

Author: omkarlanghe

math/check_prime.cpp

@@ -0,0 +1,58 @@
+/**
+ * Copyright 2020 @author omkarlanghe
+ *
+ * @file 
+ * A simple program to check if the given number if prime or not.
+ * 
+ * @brief
+ * Reduced all possibilities of a number which cannot be prime.
+ * Eg: No even number, except 2 can be a prime number, hence we will increment our loop with i+2 jumping on all odd numbers only.
+ * If number is <= 1 or if it is even except 2, break the loop and return false telling number is not prime.
+ */
+#include <iostream>
+#include <cassert>
+ /**
+ * Function to check if the given number is prime or not.
+ * @param num number to be checked.
+ * @return if number is prime, it returns @ true, else it returns @ false.
+ */
+template<typename T>
+bool is_prime(T num) {
+    bool result = true;
+    if (num <= 1) {
+        return 0;
+    } else if (num == 2) {
+        return 1;
+    } else if ((num & 1) == 0) {
+        return 0;
+    }
+    if (num >= 3) {
+        for (T i = 3 ; (i*i) < (num) ; i = (i + 2)) {
+            if ((num % i) == 0) {
+                result = false;
+                break;
+            }
+        }
+    }
+    return (result);
+}
+
+/**
+ * Main function
+ */
+int main() {
+    int num;
+    std::cout << "Enter the number to check if it is prime or not" <<
+    std::endl;
+    std::cin >> num;
+    bool result = is_prime(num);
+    if (result) {
+        std::cout << num << " is a prime number" <<
+        std::endl;
+    } else {
+        std::cout << num << " is not a prime number" <<
+        std::endl;
+    }
+    assert(is_prime(50) == false);
+    assert(is_prime(115249) == true);
+}