C++ | Mathematic

[drk]

Hi guys!

I started learning these days and I need know this:

int a = 1, b = 2, c = 3; 
int result = ++a/a&&!b&&c||b--||-a+4*c>!!b; 

I know that it's needed to put two equal symbols to the system understand that it's to write "!!" and not use "!", but I can't understand this: c>!!b.

Someone, help me please and sorry for can't explain good.

[karlis]

i think it'll output 2, cause 1st will be false, but b-- is still 2.

[drk]

Thanks for answering, but I wanna know only "c>!!b"

[karlis]

that's just a not not, resulting in false if b is false, or true if statement is any other value.

im not experienced with C++, therefore i cant say would it cause errors, but boolean comparison to other size seems wrong to me.

[drk]

Okay. Thanks, now can someone explain me in this code:

void main() 
{ 
    int i, j, k; 
    printf ( "\n" ); 
    for ( k = 0; k <= 1; k++ ) 
    { 
        printf ( "\n" ); 
        for ( i = 1; i < 5; i++ ) 
            printf ( "Tabuada do %3d      ", i + 4 * k + 1 ); 
            printf ( "\n" ); 
            for ( i = 1; i <= 9; i++ ) 
            { 
                for ( j = 2 + 4 * k; j <= 5 + 4 * k; j++ ) 
                    printf ( "%3d x%3d = %3d     ", j, i, j * i ); 
                    printf ( "\n" ); 
            } 
    } 
} 

Why just in 2 for loops it's needed keys { } ?

[Kenix]

It's optional use { } in for loop.

#include <iostream> 
  
int main( ) 
{ 
    for ( int i = 0; i < 5; i++ ) 
        printf( "%d \n", i ); 
    return 0; 
} 

Output:

  
0 
1 
2 
3 
4 
  

Also

#include <iostream> 
  
int main() 
{ 
    int i = 10; 
    if ( i ) 
        printf( "%d \n", i ); 
    return 0; 
} 

Output:

10 

You can test it here: http://codepad.org/

Also you need better read documentation about c++

Edited April 13, 2012 by Guest

[drk]

k Thanks, I understand now.

[drk]

It's optional use { } in for loop.

#include <iostream> 
  
int main( ) 
{ 
    for ( int i = 0; i < 5; i++ ) 
        printf( "%d \n", i ); 
    return 0; 
} 

Output:

  
0 
1 
2 
3 
4 
  

Also

#include <iostream> 
  
int main() 
{ 
    int i = 10; 
    if ( i ) 
        printf( "%d \n", i ); 
    return 0; 
} 

Output:

10 

You can test it here: http://codepad.org/

Also you need better read documentation about c++

Also you need better read documentation about c++

I'm already learning C++ from a book I bought and It has much exercises and these things but don't explain somethings.

[drk]

I don't know if I must create a new topic for this, so here we go:

#include "stdafx.h" 
#include <Windows.h> 
#include <stdint.h> 
  
int main() 
{ 
    int nPrimo; 
    int bPrimo = 0; 
    printf ( "Type a number: " ); 
    scanf_s ( "%d", &nPrimo ); 
    for ( int i = 2; i <= nPrimo; i++ ) 
    { 
        if ( nPrimo%i != 0 )  
        { 
            bPrimo = 1; 
        } 
                 
        if ( bPrimo == 0 ) 
        { 
            MessageBox ( NULL, L"The number is prime!", L"Information", MB_ICONQUESTION ); 
            return 0; 
        } 
        else 
        { 
            MessageBox ( NULL, L"The number is not prime!", L"Information", MB_ICONQUESTION ); 
            return 1; 
        }    
    } 
} 

I made this ( classes exercise ), It works now, but if number is 3 it says number is not prime lol

I don't know why, can someone help?

I can't understand this shitty prime numbers

[karlis]

it fist checks 2, and outputs what happened to 2, not whole loop.

[drk]

I know, but anyway 3 / 2 = 1,5, not 1.

[karlis]

it first checks 2 with 3, and 3%2 = 1 therefore not 0, then it returns without checking other values.

[drk]

No. 3 % 2 returns 0 lol

3,0   | 2 
1 0     1,5 
  0    

Rest -> 0

[karlis]

3/2 = 1 and remainder 1

Edited April 14, 2012 by Guest

[drk]

3/2 = 2 and remainder 1

I can't understand how can this be 1 if division 3 / 2 returns result 1,5

Edit: Oh, awesome! I understand now why is that returning 1. Thanks, I solved the problem.

[karlis]

3/2 = 1, remainder 1 **

[drk]

Thanks for helping.