Objective c == strings and isEqualToString method not finding match [closed] - objective-c

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Closed 10 years ago.
I am trying to find out if a 1 letter string appears in the first 2 letters of a different string. I have tried to compare the strings with == as well as the isEqualToString NSString method.
Does anyone have any idea why my code is not able to find a match. It always just returns 0.
I am wanting the methods to be returning 2 as the letter b is in the second letter location in the word (first parameter) and should match the letter (second parameter)
main method:
Finder *f = [[Finder alloc]init];
int position = [f findLetterLocation : #"abc" : #"b"];
NSLog(#"using == %d", position);
int position2 = [f findLetterLocation2 : #"abc" : #"b"];
NSLog(#"using isEqualToString %d", position);
Finder.m
-(int)findLetterLocation: (NSString*)word : (NSString*)letter{
NSRange MyOneRange = {1, 1};
NSRange MyTwoRange = {2, 1};
NSString *firstCharacter = [[NSString alloc] init];
NSString *secondCharacter = [[NSString alloc] init];
firstCharacter = [word substringWithRange:MyOneRange];
secondCharacter = [word substringWithRange:MyTwoRange];
if(firstCharacter == letter){
return 1;
}
if(firstCharacter == letter){
return 2;
}
return 0;
}
findLetterLocation2 is exactly the same as the method above but only replaces the if statements with the ones below:
if([firstCharacter isEqualToString: letter]){
return 1;
}
if([firstCharacter isEqualToString: letter]){
return 2;
}
The output is
2012-12-29 18:14:51.253 test[83101:303] using == 0
2012-12-29 18:14:51.255 test[83101:303] using isEqualToString 0
Thanks!

Answer 1

You're defining a method -[Finder findLetterLocation::]. You want this method to return the 1-indexed location in the first argument ("word") of the second argument ("letter") if it is the first or second letter and otherwise return 0. This implementation will do the trick:
-(int)findLetterLocation: (NSString*)word : (NSString*)letter
{
int res = 0;
if (word &&
letter &&
[letter length] == 1) {
NSRange range = [word rangeOfString:letter];
if (range.location < 2) {
res = range.location + 1;
}
}
return res;
}
This method name is unconventional. A better method name would be
- (int)locationInString:(NSString *)string ofLetter:(NSString *)letter
A still better method name would be
- (int)pfx_oneIndexedLocationInFirstTwoCharactersOfString:(NSString *)string ofCharacter:(NSString *)letter
where pfx is replaced with your project's prefix.
This method's return type should not be int. Instead it should be either NSUInteger or NSInteger, probably NSUInteger since the result will always be 0, 1 or 2.
- (NSUInteger)pfx_oneIndexedLocationInFirstTwoCharactersOfString:(NSString *)string ofCharacter:(NSString *)letter
This method should probably be in a category on NSString rather than in a stand-alone class Finder:
#interface NSString (Locating)
- (NSUInteger)pfx_oneIndexedLocationInFirstTwoCharactersOfCharacter:(NSString *)character
#end
#implementation NSString (Locating)
- (NSUInteger)pfx_oneIndexedLocationInFirstTwoCharactersOfCharacter:(NSString *)character
{
int res = 0;
if (character &&
[character length] == 1) {
NSRange range = [word rangeOfString:letter];
if (range.location < 2) {
res = range.location + 1;
}
}
return res;
}
#end

Answer 2

NSRange uses location as index 0. the characters you are getting are character 2 and character 3.
Also. I believe that NSString will only match with == if you use the same object.
To match strings use -[NSString isEqualToString:]
Hope that helps
You can test with
NSLog(#"First Character = %#", firstCharacter);