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  1. #include <iostream>
  2. #include <cmath>
  3.  
  4. int main()
  5. {
  6.     using namespace std ;
  7.  
  8.     //initialize some long ass integers
  9.     long long primeanswer = 1,p = 1,sqrt_of_i;
  10.     //flag for counting a discovery of a factor
  11.     int factorcount = 0;
  12.     //for loop counts down in twos from an odd number i is number to check
  13.     for (long long i=74;i>0; i=i-2)
  14.     {
  15.         //reset factor count flag to zero
  16.         factorcount =0;
  17.         //squaring i means that finding a factor of i wont take as long
  18.         sqrt_of_i = sqrt(i);
  19.         //loop usues p to get numbers fo checking against square of i
  20.         for(long long p=1; p<=sqrt_of_i; p++ )
  21.         {
  22.             //if there is a remainder of 0 when diveded...
  23.             if((i%p)==0)
  24.             {
  25.                 //then a factor has been found, the integer is incremented
  26.                 factorcount++;
  27.                 //if there is more than two factors the we are not dealing with a prime
  28.                 if(factorcount>=2)
  29.                     {
  30.                         break;
  31.                     }
  32.             }
  33.  
  34.         }
  35.         //if we found only one factor (1) then we output the prime :D
  36.         if(factorcount<=1)
  37.         {
  38.             primeanswer = i;
  39.                cout<<primeanswer<<" ";
  40.         }
  41.     }
  42.  
  43. }
Success #stdin #stdout 0s 2684KB
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https://ideone.com/EyOa8e
language:
C++ 4.3.2 (gcc-4.3.2)
created:
11 years ago
visibility:
public

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