Raj Valand Code Added

prime-number.cpp

@@ -2,64 +2,29 @@
  *
  *  a program that tests if a given integer is prime
  *
- *  Author: cmhughes
- *  Date:   November 18th, 2016
+ *  Author: Raj Valand
+ *  Date:   September 24th, 2020
  *
  *  Input: user is requested for a number, n; 
- *
- *  Output: the program details all of the 
- *          integers <= n, tests them to see if they 
- *          are prime, and gives a 1/0 for prime/not prime respectively
- *  
- *  reference: https://en.wikipedia.org/wiki/Primality_test#Pseudocode
- *
  */
-#include <iostream>
-#include <cassert>
-#include <cmath>
-
-int main() {
-    // declare the is_prime routine
-    int is_prime(int integer_to_be_tested);
-    int maximum_integer;
-    int total_primes_in_range = 0;
-
-    // request user input, and validate
-    std::cout << "Enter a integer:\n";
-    std::cin >> maximum_integer;
-    assert(maximum_integer > 0);
-
-    // loop through from 1 to maximum integer
-    for(int i=1; i<=maximum_integer; i++){
-        std::cout << "is " << i << " prime? " << is_prime(i) << "\n";
-        is_prime(i) ? total_primes_in_range++ : 0;
-    }
-
-    std::cout << "Total number of prime numbers from 1 to " << maximum_integer << " is: " << total_primes_in_range;
-    return (0);
-}
-
-int is_prime(int integer_to_be_tested){
-    assert(integer_to_be_tested > 0);
-    switch (integer_to_be_tested){
-        case 1:
-            return 1;
-        case 2:
-            return 1;
-        case 3:
-            return 1;
-        default:
-            // if the integer is even, return immediately
-            if(integer_to_be_tested % 2 == 0){
-                return 0;
-            }
+#include<bits/stdc++.h>
+using namespace std;
 
-            // otherwise, proceed with the alogorithm
-            for(int i=2; i<=sqrt(integer_to_be_tested); i++){
-                if( (integer_to_be_tested % i)==0 or (integer_to_be_tested % (i+2)) ==0 ){
-                    return 0;
-                }
-            }
-            return 1;
-    }
-}
+int main(){
+	int n;
+	cin>>n;
+	int a[n];
+	for(int i=0;i<n;i++)
+		a[i] = 0;
+	for(int i=2;i<=sqrt(n);i++){
+		for(int j = i+1;j<=n;j++){
+			if(j%i == 0)
+				a[j] = 1;
+		}
+	}
+	for(int i=2;i<=n;i++){
+		if(a[i]==0)
+			cout<<i<<endl;
+	}
+	return 0;
+}