NSString with special character

[architectpianist]

Hi all,
I'm trying to write a program to graph polar functions. The problem is, I don't know how to detect the theta (θ) symbol. I'm parsing the expression manually (characterAtIndex of NSString). So if characterAtIndex doesn't work for θ, then is there a method I can use to find it?
Thanks!

[aziz]

You can use:

NSArray *arr =[myString componentsSeparatedByString:@"θ"];

[Duncan C]

Originally Posted by architectpianist

Hi all,
I'm trying to write a program to graph polar functions. The problem is, I don't know how to detect the theta (θ) symbol. I'm parsing the expression manually (characterAtIndex of NSString). So if characterAtIndex doesn't work for θ, then is there a method I can use to find it?
Thanks!

I used this code to figure out the numeric value of a theta character:

  NSString* test = @"θ";
  unichar testChar = [test characterAtIndex: 0];
  NSLog(@"theta %d", testChar);

The result I got was "theta 952"

So a theta has a numeric value of 952.

You could also search for a theta like any other string using one of the NSString search methods, like rangeOfString:

[architectpianist]

I decided to use rangeOfString. But looking at the documentation, it says that rangeOfString returns:

An NSRange structure giving the location and length in the receiver of the first occurrence of aString. Returns {NSNotFound, 0} if aString is not found or is empty (@"").

I'm not very experienced at NSRanges, how do I determine if the return value is not NSNotFound? I assume I can't use !=?
I've also tried

if ([[string substringFromIndex:i] rangeOfString:@"θ"].location != NSNotFound)

but this is not being called when I type in "2θ".
Thanks for your reply!

[Duncan C]

Originally Posted by architectpianist

I decided to use rangeOfString. But looking at the documentation, it says that rangeOfString returns:

I'm not very experienced at NSRanges, how do I determine if the return value is not NSNotFound? I assume I can't use !=?
I've also tried

if ([[string substringFromIndex:i] rangeOfString:@"θ"].location != NSNotFound)

but this is not being called when I type in "2θ".
Thanks for your reply!

Do it like this:

NSRange range;

range = [string rangeOfString:@"θ"];
if (range.location != NSNotFound)
{
  //there was a theta in the string
}

Doing it all in one, with

if ([string rangeOfString:@"θ"].location != NSNotFound)

should work too, but then if the theta is found, you'd have to repeat the search to figure out where it is. The code you posted looks like a muddle.

[architectpianist]

Doing it like this:

NSString *substring = [string substringFromIndex:i];
NSLog(@"substring is %@", sstring);
NSRange range = [substring rangeOfString:@"θ"];
NSLog(@"Range: %i, %i", range.location, range.length);
if (range.location != NSNotFound)
{
	//do stuff with theta
}

in fact returns an NSNotFound (2147483647) for range.location. The substring turns up as ∏, which is totally wrong.
Am I doing something wrong here? Where did the ∏ come from???

[Duncan C]

Originally Posted by architectpianist

Doing it like this:

NSString *substring = [string substringFromIndex:i];
NSLog(@"substring is %@", sstring);
NSRange range = [substring rangeOfString:@"θ"];
NSLog(@"Range: %i, %i", range.location, range.length);
if (range.location != NSNotFound)
{
	//do stuff with theta
}

in fact returns an NSNotFound (2147483647) for range.location. The substring turns up as ∏, which is totally wrong.
Am I doing something wrong here? Where did the ∏ come from???

You're getting all confused.

Don't use substringFromIndex and rangeOfString. Just use the few lines of code I posted.

rangeOfString will search an arbitrary-sized string and let you know if a substring appears inside.

[architectpianist]

Well, I fixed it, but I don't get why.

I used:

NSRange range = [string rangeOfString:@"∏"];
if (range.location != NSNotFound)
{
	NSLog(@"Adding a θ");
}

Yeah, the ∏ seems kind of strange, but that's what shows up in the string when I type in the theta.
Any explanations?
And thanks for the fast replies, Duncan!

[architectpianist]

I'm now having another issue with these darned special characters.

I want to display the functions in a Recents menu. But when I take the strings directly, they contain the uppercase pi, not the lowercase theta.

What I'm doing is really simple:

for (NSString *function in self.recentFunctions) 
{
	function = [function stringByReplacingOccurrencesOfString:@"Π" withString:@"θ"];
}

But immediately after this code is run, an NSLog shows that no change has been made to the array. I also get a memory warning about this time. In fact, logging

NSLog(@"Recent functions: %@", self.recentFunctions);

gives an array where every pi character is replaced by \U220f. I tried replacing the pi character in the stringByReplacingOccurrencesOfString method with \u220f, but that doesn't work either. However, by using NSString's rangeOfString with \u220f, it does tell me that that character is present. The table view displays the character as an uppercase pi.

Why do these special characters have to be so pesky? And why is the stringByReplacingOccurrencesOfString method not working in this case?
Thanks for your help!