From 45a9b582f32478bae47830baf4d864527af68e44 Mon Sep 17 00:00:00 2001
From: prashansa15 <prashansa15111784@gmail.com>
Date: Wed, 6 Oct 2021 12:59:12 +0530
Subject: [PATCH] sieve of eartosthenes added

---
 CPP Programs/sieveOfEartosthenes.cpp | 50 ++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 CPP Programs/sieveOfEartosthenes.cpp

diff --git a/CPP Programs/sieveOfEartosthenes.cpp b/CPP Programs/sieveOfEartosthenes.cpp
new file mode 100644
index 0000000..5469858
--- /dev/null
+++ b/CPP Programs/sieveOfEartosthenes.cpp	
@@ -0,0 +1,50 @@
+/* 
+    This program is used to print all the 
+    prime numbers less than or equal to
+    a given number n.
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+ 
+void SieveOfEratosthenes(int n){
+    // Create a boolean array
+    // "prime[0..n]" and initialize
+    // all entries it as true.
+    // A value in prime[i] will
+    // finally be false if i is
+    // Not a prime, else true.
+    bool prime[n + 1];
+    memset(prime, true, sizeof(prime));
+ 
+    for (int p = 2; p * p <= n; p++){
+
+        // If prime[p] is not changed,
+        // then it is a prime
+        if (prime[p] == true){
+            // Update all multiples
+            // of p greater than or
+            // equal to the square of it
+            // numbers which are multiple
+            // of p and are less than p^2
+            // are already been marked.
+            for (int i = p * p; i <= n; i += p)
+                prime[i] = false;
+        }
+    }
+ 
+    // Print all prime numbers
+    for (int p = 2; p <= n; p++)
+        if (prime[p])
+            cout << p << " ";
+}
+ 
+// Driver Code
+int main(){
+    int n;
+    cin >> n;
+    cout << "Following are the prime numbers smaller "
+         << " than or equal to " << n << endl;
+    SieveOfEratosthenes(n);
+    return 0;
+}