Why I Can't Output All Result On Computer? But On The Phone Use C4droid Can Output All Result (The 7Th Line 'For(J=2;J<I;J++)' Don't Have '>',)

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C++

#include"stdio.h"
main()
{
  int i, j;
  for(i=2;i<32767;i++)
  {   
    for(j=2;j<i;j++)
    {
      if ((i%j)==0 ) break;
    }
 
    if (i==j)  printf("%d\n",i);
  }

  return 0;
}

Posted 7-Apr-15 14:21pm

panlincong

Updated 7-Apr-15 15:37pm

PIEBALDconsult

v3

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Comments

BacchusBeale 7-Apr-15 20:48pm

Looks right to me. Maybe use INT_MAX instead of 32767, in case highest int differs between machines?

Sergey Alexandrovich Kryukov 7-Apr-15 21:16pm

Right. I would not even allow 2 to be written twice. Immediate constants are bad, explicit constants (or #define) should be used.
The algorithm does not look reasonable...
—SA

panlincong 8-Apr-15 5:27am

your word is very correct ,i didn't pay attention to it,the length of'int' is not regular,it depend on machine,i will use 'long' or 'short',thank you;

Mohibur Rashid 7-Apr-15 21:00pm

Probably, because of your compiler settings. besides it would print from 2~32766, so the logic in not meaningful

PIEBALDconsult 7-Apr-15 21:13pm

Yuck, trying to find prime numbers the hardest way possible?
I don't see a problem; which values are and are not displayed?
Seems OK on my system.

Sergey Alexandrovich Kryukov 7-Apr-15 21:17pm

What are you trying to achieve with that? The algorithm does not look reasonable...
What, different results on different platforms? Hard to believe...
—SA

panlincong 8-Apr-15 5:51am

i will pay attention to make my code more normative .c4-droid is a app of android to write code,i use it run the same code,it can output all result,but on computer ,only output some of all prime number ,the first prime number is not 2,but is 29629.is it because of the difference of machine?

panlincong 8-Apr-15 6:08am

how i can avoid hard-code? sometimes i want to define a constants,for example,#define price 34,the code is ok or not workable,i read some information said that code
of standard ban to use hard-code,if i want to define a word to constants how should i do?

Sergey Alexandrovich Kryukov 8-Apr-15 10:36am

You need to declare constant explicitly. Depending on C dialect, you can use constant definitions:
int const startingIndex = 2;

in all cases, you can use pre-processor #define, as I already mentioned:

#define startingIndex 2

Each time you have some constant value mentioned immediately in code twice, you take a risk of nasty bugs and unwanted labor. Your algorithm assumes that these values are the same, and eventually you want to change them. How to change them all consistently? You can easily change N of M and forget about remaining M − N...

—SA

Sergey Alexandrovich Kryukov 8-Apr-15 10:37am

Now, my questions:
Why C, why not C++?
What are you trying to achieve with the code you've shown?
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-04-07T15:28:00

Look, if i == 3, inner loop with start with 2 and go to 2, and 2%2 will give you 0 and hence the break from the inner loop. From this point, you will go to 3%3, 4%4, never reaching 4%2 == 0, 6%2 == 0 and so on, because the cases with i == j come sooner, followed the bread statement. It should tell you that the algorithm is superfluous for the results it gives you. So, I would assume you tried to achieve something else.

No matter what you do, in any case and even a slightest concern of your runtime, you need to use the debugger.

The only difference between different platform you might have is the size of the type int. By the way, for this problem you should better use unsigned types.

Don't use so short one-letter names. All names should be correct English words without abbreviations, and the words should reflect the purpose of the variables/members/types; it greatly helps maintenance.

Never hard-code immediate constants like 32767 or 2, especially is you repeat them in code. Please see the first comment to the question and my response comment. (I would make exclusion for such constants as 0 and 1.)

—SA