Merge pull request #143 from bhutianimukul/main

added code for primes and sieve of eranthosis

prime.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <cmath>
+#include <cstring>
+using namespace std;
+bool checkPrime(int n)
+{
+    for (int i = 2; i * i <= n; i++)
+    {
+        if (n % i != 0)
+            return false;
+    }
+    return true;
+}
+void sieveOfEran(int n)
+{   // time complexity
+    // n * log(log(n))
+    bool arr[n + 1];
+    memset(arr, true, n + 1);
+
+    for (int i = 2; i * i <= n; i++)
+    {
+        cout << " i" << i << ":" << arr[i] << endl;
+        if (arr[i] == true)
+        {
+            for (int j = 2 * i; j <= n; j = j + i)
+            {
+                arr[j] = false;
+            }
+        }
+    }
+    for (int i = 0; i <= n; i++)
+    {
+        cout << i << ":" << arr[i];
+        cout << "\n";
+    }
+}
+int main()
+{
+    int n = 12;
+    sieveOfEran(10);
+}