Initial commit. Various versions of a prime number generator.

primes1.cpp

@@ -0,0 +1,32 @@
+//Finding all of the prime numbers between 1 and n.
+//First crack at it. very inefficient.
+
+#include <iostream>
+#include <stdlib.h>
+
+using namespace std;
+
+bool isPrime(int num) {
+  bool prime = true;
+  if (num < 2)
+    return false;
+  for (int i = 2; i < num; ++i) {
+    if (num % i == 0)
+      prime = false;
+  }
+  return prime;
+}
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+  for (int j = 0; j <= TOP; ++j) {
+    if (isPrime(j))
+      std::cout << j << " ";
+  }
+  std::cout << std::endl;
+  return 0;
+}

primes2.cpp

@@ -0,0 +1,33 @@
+
+//Finding all of the prime numbers between 1 and n.
+//First crack at it. very inefficient.
+
+#include <iostream>
+#include <stdlib.h>
+
+using namespace std;
+
+bool isPrime(int num) {
+  bool prime = true;
+  if (num < 2)
+    return false;
+  for (int i = 2; i < num; ++i) {
+    if (num % i == 0)
+      return false;
+  }
+  return true;
+}
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+  for (int j = 0; j <= TOP; ++j) {
+    if (isPrime(j))
+      std::cout << j << " ";
+  }
+  std::cout << std::endl;
+  return 0;
+}

primes3.cpp

@@ -0,0 +1,31 @@
+#include <iostream>
+#include <stdlib.h>
+
+using namespace std;
+
+bool isPrime(int num) {
+  bool prime = true;
+  if (num < 2)
+    return false;
+  //reduce the range of numbers being checked to half of the num.
+  for (int i = 2; i < (num/2)+1; ++i) {
+    //std::cout << num << " / " << i << " = " << num % i << std::endl;
+    if (num % i == 0)
+      return false;
+  }
+  return true;
+}
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+  for (int j = 0; j <= TOP; ++j) {
+    if (isPrime(j))
+      std::cout << j << " ";
+  }
+  std::cout << std::endl;
+  return 0;
+}

primes4.cpp

@@ -0,0 +1,33 @@
+#include <iostream>
+#include <stdlib.h>
+#include <math.h>
+
+using namespace std;
+
+bool isPrime(int num) {
+  bool prime = true;
+  if (num < 2)
+    return false;
+  double maxDivisor = pow((double)num+1, 0.5);
+  for (int i = 2; i <= (int)maxDivisor; ++i) {
+    if (num % i == 0)
+      return false;
+  }
+  return true;
+}
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+  for (int j = 0; j <= TOP; ++j) {
+    if (isPrime(j))
+      std::cout << j << " ";
+  }
+  std::cout << std::endl;
+  return 0;
+}
+
+

primes5.cpp

@@ -0,0 +1,29 @@
+#include <iostream>
+#include <stdlib.h>
+
+using namespace std;
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+
+  bool* sieve = new bool[TOP+1];
+  std::fill_n(sieve, TOP+1, 1);
+  sieve[0] = 0;
+  sieve[1] = 0;
+  for (int i = 2; i <= TOP; ++i) {
+    if (sieve[i] == 1) {
+      std::cout << i << " ";
+      for (int j = i; j <= TOP; j+=i) {
+        sieve[j] = 0;
+      }
+    } 
+  }
+  delete[] sieve;
+  return 0;
+}
+
+

primes6.cpp

@@ -0,0 +1,33 @@
+#include <iostream>
+#include <stdlib.h>
+#include <math.h>
+
+using namespace std;
+
+int main(int argc, char *argv[])
+{
+  if (argv[1] == NULL)
+    return 0;
+  const int TOP = atoi(argv[1]);
+  std::cout << "Prime Numbers from 0 - " << TOP << ": ";
+
+  const int newTop = ((TOP/2)-1+TOP%2);
+
+  //cout << newTop << endl;
+  bool* sieve = new bool[newTop+1];
+
+  std::fill_n(sieve, newTop+1, 1);
+
+  for (int i = 2; i <= (int)pow(newTop, 0.5); ++i) {
+    if (sieve[i] == 0) {
+      std::cout << i << " ";
+      for (int j = i; j <= TOP; j+=i) {
+        sieve[j] = 0;
+      }
+    } 
+  }
+  delete[] sieve;
+  return 0;
+}
+
+