C / C++ / MFC

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

Ian Darling13-Jul-03 23:33

Ian Darling

13-Jul-03 23:33

strcmp returns a negative or positive number if the first string is less than or greater than the second string (check which way round they actually are in MSDN), which is why it returns 0 for equality.

--
Ian Darling

get mouse coordinate

henli13-Jul-03 18:36

henli

13-Jul-03 18:36

I am trying to get the mouse coodinate on picture box/control while mouse click accour on it in order to draw some circle based on that coordinate. But so far I can get it. I can get the mouse coordinate only on form itseft not on picture box.

Any one can help me?I really appreciate it, thank you.

Re: get mouse coordinate

Nick Parker13-Jul-03 19:13

Nick Parker

13-Jul-03 19:13

Try GetCursorPos() function, you just pass it a pointer to a POINT structure.

-Nick Parker

Re: get mouse coordinate

Ryan Binns13-Jul-03 22:53