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  1. // Nicolas Ruano           CS1A          Chapter 6, P. 375, #21 
  2.  
  3. // 
  4.  
  5. /******************************************************************************* 
  6. * VERIFY IF A GIVEN NUMBER IS A PRIME NUMBER. 
  7.  
  8. * ______________________________________________________________________________ 
  9.  
  10. * The program prompts the user for a number, ensures it’s  
  11. * greater than 1, then checks if it is divisible by any number 
  12. * from 2 to (number – 1). If so, it’s not prime; if not, it’s  
  13. * prime. The result is then displayed. 
  14.  
  15. * Computation is based on the formula: 
  16.  
  17. * For a number n: 
  18. * Prime(n)= 
  19. * False, if n≤1, 
  20. * False, if there exists an i such that 2≤i<n and n  mod  i=0, 
  21. * True, Otherwise 
  22.  
  23. * Where: 
  24. * n  mod  i = 0 means “n is evenly divisible by i.” 
  25.  
  26. * ______________________________________________________________________________ 
  27.  
  28. * INPUT 
  29. *   num                int    The number entered by user. 
  30. * 
  31. * 
  32. * OUTPUT 
  33. *   isPrime(num)       bool   Control which message is printed 
  34. *   num                int    The number entered by user. 
  35. *******************************************************************************/ 
  36. #include <iostream>   // Needed for input and output 
  37. using namespace std; 
  38.  
  39. // Function to check if a number is prime 
  40. bool isPrime(int number) { 
  41.     if (number <= 1) { 
  42.         return false; // Numbers less than or equal to 1 are not prime 
  43.  
  44.     } 
  45.  
  46.     // Check for factors between 2 and number - 1 
  47.     for (int i = 2; i < number; i++) { 
  48.         if (number % i == 0) { 
  49.             return false; // Found a divisor, so it's not prime 
  50.  
  51.         } 
  52.     } 
  53.  
  54.     return true; // No divisors found, it's prime 
  55. } 
  56.  
  57. int main() { 
  58.     int num; 
  59.  
  60.     cout << "Enter a number: "; 
  61.     cin >> num; 
  62.  
  63.     if (isPrime(num)) { 
  64.         cout << num << " is a prime number." << endl; 
  65.     } else { 
  66.         cout << num << " is not a prime number." << endl; 
  67.     } 
  68.  
  69.     return 0; 
  70. }
Success #stdin #stdout 0.01s 5276KB
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Enter a number: 32767 is not a prime number.
https://ideone.com/PoSWy9
language:
C++ (gcc 8.3)
created:
16 days ago
visibility:
public

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