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  1. // Nicolas Ruano           CS1A          Chapter 6, P. 375, #21 
  2. /******************************************************************************* 
  3. * VERIFY IF A GIVEN NUMBER IS A PRIME NUMBER. 
  4.  
  5. * ______________________________________________________________________________ 
  6.  
  7. * The program prompts the user for a number, ensures it’s  
  8. * greater than 1, then checks if it is divisible by any number 
  9. * from 2 to (number – 1). If so, it’s not prime; if not, it’s  
  10. * prime. The result is then displayed. 
  11.  
  12. * Computation is based on the formula: 
  13.  
  14. * For a number n: 
  15. * Prime(n)= 
  16. * False, if n≤1, 
  17. * False, if there exists an i such that 2≤i<n and n  mod  i=0, 
  18. * True, Otherwise 
  19.  
  20. * Where: 
  21. * n  mod  i = 0 means “n is evenly divisible by i.” 
  22.  
  23. * ______________________________________________________________________________ 
  24.  
  25. * INPUT 
  26. *   num                int    The number entered by user. 
  27. * 
  28. * 
  29. * OUTPUT 
  30. *   isPrime(num)       bool   Control which message is printed 
  31. *   num                int    The number entered by user. 
  32. *******************************************************************************/ 
  33. #include <iostream>   // Needed for input and output 
  34. using namespace std; 
  35.  
  36. // Function to check if a number is prime 
  37. bool isPrime(int number) { 
  38.     if (number <= 1) { 
  39.         return false; // Numbers less than or equal to 1 are not prime 
  40.  
  41.     } 
  42.  
  43.     // Check for factors between 2 and number - 1 
  44.     for (int i = 2; i < number; i++) { 
  45.         if (number % i == 0) { 
  46.             return false; // Found a divisor, so it's not prime 
  47.  
  48.         } 
  49.     } 
  50.  
  51.     return true; // No divisors found, it's prime 
  52. } 
  53.  
  54. int main() { 
  55.     int num; 
  56.  
  57.     cout << "Enter a number: "; 
  58.     cin >> num; 
  59.  
  60.     if (isPrime(num)) { 
  61.         cout << num << " is a prime number." << endl; 
  62.     } else { 
  63.         cout << num << " is not a prime number." << endl; 
  64.     } 
  65.  
  66.     return 0; 
  67. }
Success #stdin #stdout 0.01s 5312KB
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Standard input is empty
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Enter a number: 32766 is not a prime number.
https://ideone.com/zZ1cMs
language:
C++ (gcc 8.3)
created:
15 days ago
visibility:
public

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