Added program to generate prime numbers list issue ambujraj#76

prime/generateListOfPrimes.cpp

@@ -0,0 +1,54 @@
+//Program to generate prime numbers less than or equal to n (n < 100000). This is an O(n) algorithm. This algorithm is called Sieve_of_Eratosthenes (https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
+
+#include<bits/stdc++.h>
+#define lli long long int //macros
+#define loop(a,b) for(lli i=a;i<b;i++)
+
+using namespace std;
+int main()
+{
+    cout<<"Enter value of n: ";
+    lli n; //thee number till which you want to generate primes
+    cin>>n;
+
+    bool marked[n+1]; //a boolean array to mark the indexes of array. Indexes are treated as numbers. Ex. if marked[2] = 1, this means
+    //that 2 is a prime number.
+
+    loop(2,n+1) //initially  mark all numbers till n as non primes.
+    {
+        marked[i]=0;
+    }
+
+    lli inc,num,start,i=0;
+    num=2;
+    inc=2;
+    start=2;
+
+    while(inc <= n) //this loop takes all the unmarked numbers and mark their multiples as non-primes.
+    {
+        inc = start;
+        num=2*inc;
+        while(num<=n)
+        {
+            if(!marked[num])
+                marked[num]=1;
+            num+=inc;
+        }
+        i=start+1;
+        while(marked[i] && i<=n)
+        {
+            i++;
+        }
+        start=i;
+    }
+
+    i=2;
+    cout<<"All prime numbers less than equal to "<<n<<": \n";
+    while(i<=n) //print all primes.
+    {
+        if(!marked[i])
+            cout<<i<<" ";
+        i++;
+    }
+    return 0;
+}