C / C++ / MFC

14-Jul-03 1:49

You're welcome Smile | :)

YaronNir wrote:
Excellent man! works perfectly!

Cool! I didn't actually test that - just wrote it straight from the docs, so I'm happy that it works that well Big Grin | :-D

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

???

DaveE9th13-Jul-03 21:08

13-Jul-03 21:08

I'm trying to learn the alternative way of writing an IF statement. The code below returns a 0, it should be an 8 since 3<5, what am I doing wrong?

Thanks

<br />
<br />
#include <iostream><br />
<br />
using namespace std;<br />
<br />
int main()<br />
<br />
{<br />
int a = 3;<br />
int b (5);<br />
int x(0);<br />
<br />
a < b ? x == a + b : x == 9;<br />
<br />
cout<<x<<"\n\n";<br />
<br />
return 0;<br />
}<br />

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson

Cedric Moonen13-Jul-03 21:51

Cedric Moonen

13-Jul-03 21:51

You use the comparison operator (==) insted of the assignement operator.
Replace

a < b ? x == a + b : x == 9;<br />
<br />

a < b ? x = a + b : x = 9;<br />
<br />

jhwurmbach13-Jul-03 22:02

jhwurmbach

13-Jul-03 22:02

DaveE9th wrote:
a < b ? x == a + b : x == 9;
[...] what am I doing wrong?

The result is false, whichever clause is executed:
x is neither equal to a+b (that is 8) nor is x equal to 9.

If you want to assign x a value, you need to write

a < b ? x = a + b : x = 9;

My opinions may have changed, but not the fact that I am right.

DaveE9th13-Jul-03 22:25

13-Jul-03 22:25

Thanks, your both right. I'm glad it's working now.

Big Grin | :-D

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson

Miszou14-Jul-03 9:58

Miszou

14-Jul-03 9:58

DaveE9th wrote:
a < b ? x == a + b : x == 9;

You could also do this:

x = ( a < b ? a + b : 9 );

There are 10 kinds of people - those that get binary and those that don't.

Anthony_Yio15-Jul-03 1:07

Anthony_Yio

15-Jul-03 1:07

x = ( a < b ? a + b : 9 );

This is the right way.

IR data entry system

teanomilk13-Jul-03 20:32

teanomilk

13-Jul-03 20:32

hi Is possible to use C++ to wirte a promgram to transfer the data from Pc to the ir then tramit to the reciever the RS232

Re: IR data entry system

jan larsen14-Jul-03 2:34

jan larsen

14-Jul-03 2:34

Que?...

"After all it's just text at the end of the day. - Colin Davies

"For example, when a VB programmer comes to my house, they may say 'does your pool need cleaning, sir ?' " - Christian Graus

CallBack Function

rohit.dhamija13-Jul-03 19:46

rohit.dhamija

13-Jul-03 19:46

Hi,
I have often seen concept of callback funtion used in MFC.Can any body please explain What is a callback function and what is its use ?
Thanks
Rohit

Re: CallBack Function

Tibor Blazko13-Jul-03 19:59

Tibor Blazko

13-Jul-03 19:59

it is your function pointer to what you enter f.e. like argument to other function
that (other) function will call yours (call-back) if necessary
classic example is qsort - sorts array by by you defined criteria
you just need to enter data to sort and your callback function what will compare two items
the rest makes qsort not knowing about any data details
see qsort msdn example
t!

(http://www.codeproject.com/info/search.asp?target=callback&Submit1=+Search+&st=tt&qm=all[^])

Re: CallBack Function

Ryan Binns13-Jul-03 22:51

13-Jul-03 22:51

I explained this a day or two ago. Search back a bit and you should find the information.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

!strcmp

DaveE9th13-Jul-03 19:37

13-Jul-03 19:37

In the code below, I'm curious about the "!" in front of the strcmp function. I'm confused on this. In my understanding, the !strcmp is saying that IF str and Info do NOT compare, then cout the number. What am I missing hear? Thanks

#include "iostream.h"<br />
#include "string.h"<br />
<br />
int main()<br />
{<br />
	int x;<br />
	int i;<br />
	char str[80];<br />
	bool isfinished=false;<br />
	char Info [] [300] = <br />
	{<br />
		"3030-02-000-5287" , "Here is the information for this number." ,<br />
		"3030-03-000-0029" , "Here is the information for this number." ,<br />
};<br />
	while(isfinished==false)<br />
	{<br />
		cout<<"\nPlease enter a number:\n";<br />
        cin>>str;<br />
	    for(i=0; i < 4; i += 2)<br />
		if(!strcmp(str, Info[i]))<br />
		{<br />
			cout<<"\nInformation:"<<Info[i+1]<<"\n";<br />
			break;<br />
		}<br />
		    if(i == 4)<br />
			{<br />
				cout<<"Number not found.\n";<br />
			}<br />
			<br />
			cout<<"\nWould you like to check another?\n";<br />
			<br />
			{<br />
				cout<<"Enter 1 for yes, 0 for no.\n";<br />
		       (cin>>x).get(); <br />
<br />
			}<br />
			if (x==0)  isfinished=true;<br />
	}<br />
<br />
	return 0;<br />
}<br />

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson

Tibor Blazko13-Jul-03 20:03

Tibor Blazko

13-Jul-03 20:03

if(!something)
is equal to
if(something == 0)
our strcmp is executed, its return value is negated and if solution is not zero (false) than gets into if())
t!

Xander8013-Jul-03 20:10

Xander80

13-Jul-03 20:10

The strcmp function returns 0 when string1 is identical to string2. The application writes the info to screen when string1 is identical to string2.

DaveE9th13-Jul-03 21:04

13-Jul-03 21:04

So would strcmp (without the "!") return a 1(TRUE) if the two variables are equal?

Confused | :confused:

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson

Xander8013-Jul-03 21:35

Xander80

13-Jul-03 21:35

Oh no, sorry. The function returns 0 when the strings are equal. That would make:
if (!0)

So only when the strings are not equal, the code in the if statement gets executed, and the next in the info array is printed to screen (Info[i+1]).

I'm sorry, it's very early in the morning (in Holland) Sleepy | :zzz:

, and I hadn’t finished my coffee.
Unsure | :~

DaveE9th13-Jul-03 21:51

13-Jul-03 21:51

Xander80 Mentioned
So only when the strings are not equal, the code in the if statement gets executed, and the next in the info array is printed to screen (Info[i+1]).

I'm still confused Eek! | :eek:

If !strcmp returns 0(from a non compare condition), why would I want to cout anything? I would think that you want to cout when you have found a match. Hmmmmm.

Confused | :confused:

Thanks

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson

Xander8013-Jul-03 22:54

Xander80

13-Jul-03 22:54

Again I'm sorry Sleepy | :zzz:

(I must be sleeping).

When you compare 2 strings with strcmp(), this function returns 0, so strcmp("codeproject","codeproject") returns 0. That will result in if (!0). NOT 0 is 1, so when the 2 strings are identical, the result is displayed on screen with cout.

Check by watching the result var in the debugger:

<br />
int result = strcmp(str, Info[i]);<br />
<br />
if(!result)<br />
{<br />
	cout<<"\nInformation:"<<Info[i+1]<<"\n";<br />
	break;<br />
}

If result == 0 then the information is displayed.

Maybe it's better to rewrite the code to:

<br />
<br />
if (strcmp(str, Info[i])==0)<br />
{<br />
	cout<<"\nInformation:"<<Info[i+1]<<"\n";<br />
	break;<br />
}<br />
<br />

so it's perfectly clear that the if statement checks for identical strings (for less experienced programmers like me Unsure | :~

Ryan Binns13-Jul-03 23:13

13-Jul-03 23:13

strcmp() returns 0 when the two strings are identical. !strcmp() will invert that (! is the not operator) so it will return 1 when the strings are equal, and 0 when they are not. In this case, whatever is in the if statement will be executed when the two strings are identical.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Rob Caldecott13-Jul-03 23:17

Rob Caldecott

13-Jul-03 23:17

Bad programming practise IMHO - you should only use ! on a boolean expression - not on something that returns an int. I would always write code like this as "if (strcmp(psz1, psz2) == 0" or "if (strcmp(psz1, psz2) != 0".

Just my 2c.

When I am king, you will be first against the wall.

Ryan Binns13-Jul-03 23:22

13-Jul-03 23:22

Robert Edward Caldecott wrote:
Bad programming practise IMHO

Agreed.

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

DaveE9th13-Jul-03 23:29

13-Jul-03 23:29

Thank you all, I get it now. I was thinking that the strcmp function would return a 1 for a match, not a 0. Is there a particular reason for this? Thanks again, Dave

Big Grin | :-D

"The man who reads nothing is better educated than the man who reads nothing but newspapers."- Thomas Jefferson