Ok, so I'm trying to check if an object from an NSArray equals something inputed by the User into a UITextField. It should work, but for some reason it dosn't. Here is my code:
if (theAnswer.text == [correctAnswers objectAtIndex:problemNumber]) {
NSLog(#"CORRECT");
}
else {
NSLog(#"wrong");
}
The console always give wrong.
I put this log in:
NSLog(#"%# %#", theAnswer.text, [correctAnswers objectAtIndex:problemNumber]);
And I get A A
wrong
printed everytime. Thanks for the help
Objective-C doesn't support the == operator for NSStrings. That will do a comparison of the pointers to the NSStrings and not the contents of the string itself.
Try
if([theAnswer.text isEqualToString:[correctAnswers objectAtIndex:problemNumber]]) {
}
Related
I m taking a NSMutabledictionary object in NSString like this :
NSString *state=[d valueForKey:#"State"];
Now sometimes state may be null and sometimes filled with text.So Im comparing it.While comparing state becomes NSString sometimes and NSCFString othertimes..So unable to get the desired result..
if([state isEqualToString#""])
{
//do something
}
else
{
//do something
}
So while comparing it is returning nil sometimes.So immediately jumping into the else block.
I need a standard way to compare if the state is empty whether it is a NSString or NSCFString ...
How can I do it?
If you're unable to get the result you want, I can assure you it's not because you get a NSCFString instead of a NSString.
In Objective-C, the framework is filled with cluster classes; that is, you see a class in the documentation, and in fact, it's just an interface. The framework has instead its own implementations of these classes. For instance, as you noted, the NSString class is often represented by the NSCFString class instead; and there are a few others, like NSConstantString and NSPathStore2, that are in fact subclasses of NSString, and that will behave just like you expect.
Your issue, from what I see...
Now sometimes state may be null and sometimes filled with text.
... is that in Objective-C, it's legal to call a method on nil. (Nil is the Objective-C concept of null in other languages like C# and Java.) However, when you do, the return value is always zeroed; so if you string is nil, any equality comparison to it made with a method will return NO, even if you compare against nil. And even then, please note that an empty string is not the same thing as nil, since nil can be seen as the absence of anything. An empty string doesn't have characters, but hey, at least it's there. nil means there's nothing.
So instead of using a method to compare state to an empty string, you probably need to check that state is not nil, using simple pointer equality.
if(state == nil)
{
//do something
}
else
{
//do something
}
You can do this
if([state isEqualToString:#""])
{
//do something
}
else
{
//do something
}
You must have to type cast it to get the correct answer.
NSString *state = (NSString *) [d valueForKey:#"State"];
if(state != nil)
{
if(state.length > 0)
{
//string contains characters
}
}
I am new in the game, so probably an easy issue. What I am trying to do is to make an app with a question asked, and a textFiled in which to answer. Then, i want the app to recognize when the answer is right (in this case the number 25) and when it is wrong (not 25). Everything is working fine, and I get the "wrong" message, but I cant make it recognize the right answer.
- (IBAction)btnSubmitAction:(id)sender {
if (textFieldAnswer.text == #"25") {
lblAnswer.text = #"Yes, your right!";
btnNext.hidden = 0;
} else {
lblAnswer.text = #"No, try again.";
}
}
Thanks a lot!
Well, this is how you're supposed to compare strings:
- (IBAction)btnSubmitAction:(id)sender {
if ([textFieldAnswer.text isEqualToString:#"25"]) {
lblAnswer.text = #"Yes, you're right!";
btnNext.hidden = NO;
} else {
lblAnswer.text = #"No, try again.";
}
}
Comparing objects in Objective-C is done by ==. This means that you compare pointers, which is not the same as comparing strings, because they are pointers. If you would like to compare strings for equality you should call the BOOL instance method isEqualToString of NSString class.
[string1 isEqualToString:#"someString"]
I've got myself a piece of the iPhone SDK and been trying to make some simple apps. In this one, i want to compare the first character of self.label.string with the last one of ((UITextField *)sender).text. I decided to name them self.texty and self.input, respectively.
I would expect this if statement returning yes to me under certain circumstances, however I can't seem to get that done.
(in my case, my self.label.string was equal to 'hello!', while my self.input ended in an 'h'.)
self.input = [NSString stringWithFormat:#"%#", [((UITextField *)sender).text substringFromIndex:[((UITextField *)sender).text length]-1]];
self.texty = [NSString stringWithFormat:#"%#", [self.label.string substringToIndex:1]];
if (self.input == self.texty) {
return yes;
} else {
return no;
}
String comparison is not done with ==, but with one of the comparison methods of NSString.
For example:
if ([self.input compare:self.texty] == NSOrderedSame) {
if ([self.input isEqualToString:texty]) {
return yes;
} else {
return no;
}
EDIT:
Or a better version as the commenters noted:
return [self.input isEqualToString:texty];
If you're curious why the == operator doesn't work as expected, it's because you're actually comparing two scalar types (pointers to NSString objects) not the contents of the NSString objects themselves. As a result, it will return false unless the two compared NSStrings are actually the same instance in memory, regardless of the contents.
Greetings,
I'm trying to simply compare a NSString to an NSArray.
Here is my code:
NSString *username=uname.text;
NSString *regex=#"^[a-zA-Z0-9-_.]{3,20}$";
NSArray *matchArray=nil;
matchArray=[username componentsMatchedByRegex:regex];
if(matchArray[0] == "asdf"){ //this line causes the problem!
NSLog(#"matchArray %#",matchArray);
}
I get an "invalid operands to binary ==" error.
How can I compare the string?
Many thanks in advance,
You are trying to compare an NSString to a C string (char *), which is wrong. matchArray is an NSArray so you cannot treat it as a C array either, you have to use its objectAtIndex: method and pass in the index.
Use this instead:
if ([[matchArray objectAtIndex:0] isEqualToString:#"asdf"]) {
NSLog(#"matchArray %#", matchArray);
}
Addressing your comments, the reason why isEqualToString: does not show up in autocomplete is because Xcode cannot guess that matchArray contains NSStrings (it only knows it contains ids, that is, arbitrary Objective-C objects). If you really wanted to be sure, you can perform an explicit cast, but it doesn't matter if you don't:
if ([(NSString *)[matchArray objectAtIndex:0] isEqualToString:#"asdf"]) {
NSLog(#"matchArray %#", matchArray);
}
you want to use -objectAtIndex to get the array element. NOT the C array accessor syntax
try to use:
[[matchArray objectAtIndex:0] isEqualToString:#"asdf"];
anyway the string "asdf" should be #"asdf"
Could someone explain what is wrong with this "if statement"? I get:
"lvalue required as left operand of assignment".
This does not work:
if ([[prepDataArray objectAtIndex:iNDEX] boolValue] = YES) {
NSLog(#"HARD");
}
While this works:
diffQ = [[prepDataArray objectAtIndex:iNDEX] boolValue];
if (diffQ = YES) {
NSLog(#"HARD");
}
I do realize where the problem are and that the 'lvalue' indicate that i need to have something different on the left side but i do not grasp why and how to do what i want inside the 'if' statement as tried in the first example.
Would appreciate if someone nice could give me a hint :-)
if ([[prepDataArray objectAtIndex:iNDEX] boolValue] == YES) {
NSLog(#"HARD");
}
it's == not =
The first one doesn't work because you try to assign a BOOL (YES) to a message. The second one works because you try to assign a BOOL to diffQ. This is correct, but not the result you expect (comparing diffQ to YES)
Common programming error ;) I've done this a millions times
I completely agree with what #thomas said above, but let me add.
Don't compare a bool to YES. It's not that the if construct requires
if( some comparison statement ) {
....
}
That's not the case. The if construct has the following form:
if( a boolean value) {
...
}
It just happens that a comparison statement yields a boolean, so you put that in the if statement.
In your case, boolValue already gives you a bool. You don't need to compare that against YES or NO. That's like doing YES==YES or YES==NO and it's completely redundant.
Just do
if ([[prepDataArray objectAtIndex:iNDEX] boolValue]) {
NSLog(#"HARD");
}