sieve of eartosthenes added

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;
+}