CODEWITHSUNDEEP
objective-ciosios5
jtrain
jtrain

Reputation: 17

Math equations in Objective C iOS development

I am trying to develop a starter app just to get used to some of the utilities of Xcode and iOS development. I am trying to create an app that will solve the quadratic equation. I have tried to add this code under the "Calculate " button action. First I had "Calculate" just add the three inputs together. Now I am trying to make it solve the equation. This is what I put so far.

-(IBAction) Calculate {

float x = ([A.text floatValue]);  
float y = ([B.text floatValue]);
float z = ([C.text floatValue]);

total.text =[NSString alloc]initWithFormat:@"%.2f", -y+sqrtf(y*y-4*x*z)/2*x;

}

I know this is not the full equation, but this is what I have so far. The error I receive is to add a bracket where the semicolon is. How to make this more effecient? I wanted to create a solveEquation() function but I ran into problems. What can I do?

Upvotes: 0

Views: 892

Answers (2)

rob mayoff
rob mayoff

Reputation: 385590

You need more brackets!

total.text = [[NSString alloc]initWithFormat:@"%.2f", -y+sqrtf(y*y-4*x*z)/2*x];

The brackets indicate that you're sending an Objective-C message. For each message you send, you'll need one pair of brackets. Let's break it down like this:

NSString *uninitializedString = [NSString alloc];
NSString *initializedString = [uninitializedString initWithFormat:@"%.2f", x+y+z];
total.text = initializedString;

In the first line, we send the alloc message to the NSString object, which is actually a class object that knows how to allocate instances of NSString. But it does not initialize the instances. It pretty much just allocates the memory for them.

In the second line, we send a message to this allocated-but-uninitialized instance of NSString, telling it to initialize itself by formatting the template %.2f. This message returns an initialized instance of NSString.

Finally, in the third line, we use that initialized instance of NSString.

Obviously, it would be tedious to always need an intermediate variable to hold an allocated-but-not-initialized object. So we eliminate it by taking the result of the first message, and sending a message directly to it:

total.text = [[NSString alloc] initWithFormat:@"%.2f", x+y+z];

Upvotes: 3

zneak
zneak

Reputation: 138051

You need more brackets. The correct syntax is [object message], and since [NSString alloc] returns an object, you need [[NSString alloc] initWithFormat:@"%.2f", -y+sqrtf(y*y-4*x*z)/2*x] (initWithFormat: being another message).

Upvotes: 3

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