I have very little programming knowledge; only a fair bit in Visual Basic.
How do I take a value from a text field, then do some simple math such as divide the value by two, then display it back to the user in the same field?
In Visual Basic you could just do txtBoxOne.text = txtBoxOne.text / 2
I understand this question is more than one question and is very basic stuff, but I need to get my head out of Visual Basic and into where I should be :)
You can use doubleValue on NSString objects to retrieve the numeric value from a string.
There are variations on this, such as intValue, floatValue, boolValue, etc.
I suggest that you stick with the primitive type that has the longest range (double).
For example:
NSString *str1 = #"15";
NSString *str2 = #"5";
double result = [ str1 doubleValue ] / [ str2 doubleValue ];
NSString *str_result = [ NSString stringWithFormat: #"%f", result ];
Related
I am making a calculator that logs input in a label named "inputLabel' and then outputs the answer in a different label named "outputLabel" (similar to a graphing calculator). Once the user is finished entering the expression, the expression is stored in an NSString object and then parsed with the NSPredicate class and evaluated with the NSExpression class. What I have works, but I have noticed for particular operations the answers are not correct. For example, if the user types in "25/2" the calculator returns 12, which is obviously incorrect. However, if the user types in "25/2.0" or "25.0/2" the calculator returns 12.5 which is what I want. It seems that the NSExpression method 'expressionValueWithObject' is interpreting the operands as integers instead of floats. If this is the case, is there a way that I change the 'expressionValueWithObject'method to interpret the operands as floats?
Brain.m
-(float)performCalculation: (NSString *)operation
{
NSPredicate *parsed = [NSPredicate predicateWithFormat:[operation stringByAppendingString:#"=1.0"]];
NSExpression *inputExpressionParsed = [(NSComparisonPredicate *)parsed leftExpression];
NSNumber *result = [inputExpressionParsed expressionValueWithObject:inputExpressionParsed context:nil];
return [result floatValue];
}
ViewController.m
- (IBAction)equalsPressed:(id)sender
{
//self.inputLabel.text = [self.inputLabel.text stringByAppendingString:#".0"];
NSString *inputExpression = self.inputLabel.text;
self.inputLabel.text = [self.inputLabel.text stringByAppendingString:#"="];
float result = [self.brain performCalculation:inputExpression];
self.outputLabel.text = [NSString stringWithFormat:#"%g", result];
}
No, NSExpression cannot do that. You could try to append ".0" to all integer numbers
in the string before evaluating it, but the better solution is probably to use a "proper"
math expression parser, for example
https://github.com/davedelong/DDMathParser
You could iterate through the expression tree replacing the expression with the integer value (expressionType == NSConstantExpression). It depends a little bit of the features of your calculator, whether it is worth or not.
I'm trying to create NSDecimalNumber with simply format like: 123.00 with two fractional digits after dot, always. I tried use the NSFormatter and many other ways like converting float from string and creating then NSDecimalNumber from this string, but it's not working.
The problem is that I need only NSDecimalNumber in this format, not NSString or any other.
Thanks for any advice,
Paul
You may get idea from this.
float num = 123.1254546;
NSString *str = [NSString stringWithFormat:#"%.2f",num];
NSLog(#"%.2f %#",num,str);
I think you simply need to do Type Casting operation for Two times as bellow
float value = 123.562;
int myDigit = value;
it gives value 123 in myDigit variable
NSLog(#"MyDigit in Decimal = %d",myDigit);
Output is MyDigit in Decimal = 123
now if you want output like 123.000 then simply write as bellow
float valueWithZiro = myDigit;
NSLog(#"MyDigit with 000 == %3f",valueWithZiro);
Output is MyDigit in Decimal = 123.000
NSDecimalNumber, like NSNumber, cannot contain formatting information. The object structure simply doesn't support it. It represents a number, not the way the number is displayed.
You can convert it to a formatted NSString (which you say you don't want). But you can't do what you're asking.
You convert it to a formatted NSString using an NSNumberFormatter. It's the object that allows you to specify the decimal and thousands separators, number of decimal places to display, the currency symbol, etc.
Maybe you were looking to store a NSNumberDecimal with just two digits after the fraction?
If so NSDecimalNumberBehaviors is your friend.
I had a similar need and used the following:
self.decimalHandlingBehaviorForApp = [NSDecimalNumberHandler
decimalNumberHandlerWithRoundingMode:NSRoundUp
scale:2 raiseOnExactness:NO
raiseOnOverflow:NO raiseOnUnderflow:NO
raiseOnDivideByZero:YES];
Edit: added example of using it
// update the taxable total first
self.cartTaxableTotal = [self.cartTaxableTotal decimalNumberByAdding:itemAdded.priceOfItem
withBehavior:self.decimalHandlingBehaviorForApp];
I have a long string I want to retrieve from a URL and store at app launch. Later, I want to insert individual values into that string.
I'd like to do something like this:
NSString *numberLine = #"1 %# 3 %# 5 %#";
//... (later) ...
NSString *final = [NSString stringWithFormat:numberLine, #"two", #"four", #"six"];
NSLog(#"%#", final); //Should output "1 two 3 four 5 six"
I want the #"two" to be inserted into the placeholder %# that was earlier saved into numberLine.
Is there a good way to accomplish something like this?
So far my only thought is to do something like:
NSString *script = #"width = PLACEHOLDERpx";
script = [script stringByReplacingOccurrencesOfString:#"PLACEHOLDER" withString:#"12"];
What you are describing is a template. You want to leave placeholders in a string that will be filled out with data. While you could use %# and %d through a string that gets difficult as the string grows more complex. You may want to use a template library like Mustache for Objective-C. This will let you write expressions like this:
Hello {{SomeVariable}}
All you have to do is pass in an NSDictionary with keys that correspond to the data you want to render. So for the example above you might do the following:
NSString *result = [GRMustacheTemplate renderObject:[NSDictionary dictionaryWithObject:#"World" forKey:#"SomeVariable"];
fromString:#"Hello {{SomeVariable}}"
error:NULL];
This will produce a result string Hello World.
Can someone give a code example of how to right pad an NSString in objective-c please?
For example want these strings:
Testing 123 Long String
Hello World
Short
if right padded to a column width of say 12: and then a sting "XXX" is added to the end of each, it would give:
Testing 123 xxx
Hello World xxx
Short xxx
That is a 2nd column would like up.
Adam is on the right track, but not quite there. You do want to use +stringWithFormat:, but not quite as he suggested. If you want to pad "someString" to (say) a minimum of 12 characters, you'd use a width specifier as part of the format. Since you want the result to be left-justified, you need to precede the width specifier with a minus:
NSString *padded = [NSString stringWithFormat:#"%-12#", someString];
Or, if you wanted the result to be exactly 12 characters, you can use both minimum and maximum width specifiers:
NSString *padded = [NSString stringWithFormat:#"%-12.12#", someString];
2nd column of what would line up?
Given that you are on iOS, using HTML or a table view would be far more straightforward than trying to line up characters with spaces. Beyond being programmatically more elegant, it will look better, be more resilient to input data changes over time, and render a user experience more in line with expectations for the platform.
If you really want to use spaces, then you are going to have to limit your UI to a monospace font (ugly for readability purposes outside of specific contexts, like source code) and international characters are going to be a bit of a pain.
From there, it would be a matter of getting the string length (keeping in mind that "length" does not necessarily mean "# of characters" in some languages), doing a bit of math, using substringWithRange: and appending spaces to the result.
Unfortunately, Objective-C does not allow format specifiers for %#. A work-around for padding is the following:
NSString *padded = [NSString stringWithFormat:#"%#%*s", someString, 12-someString.length, ""];
which will pad the string to the right with spaces up to a field length of 12 characters.
%-# does not work, but %-s works
NSString *x = [NSString stringWithFormat:#"%-3#", #"a" ];
NSString *y = [NSString stringWithFormat:#"%-3#", #"abcd" ];
NSString *z = [NSString stringWithFormat:#"%-3# %#", #"a", #"bc" ];
NSString *zz = [NSString stringWithFormat:#"%-3s %#", "a", #"bc" ];
NSLog(#"[%#][%#][%#][%#].......", x,y,z,zz);
output:
[a][abcd][a bc][a bc].......
Try below. its working for me.
NSString *someString = #"1234";
NSString *padded = [someString stringByPaddingToLength: 16 withString: #"x" startingAtIndex:0];
NSLog(#"%#", someString);
NSLog(#"%#", padded);
First up, you're doing this a bad way. Please use separate labels for your two columns and then you will also be able to use proportional fonts. The way you're going about it you should be looking for an iPhone curses library.
If you really have to do it this way just use stringWithFormat:, like:
NSString *secondColumnString = #"xxx";
NSString *spacedOutString = [NSString stringWithFormat:#"testingColOne %#", secondColumnString];
NSString *spacedOutString = [NSString stringWithFormat:#"testingAgain %#", secondColumnString];
I have strings that look about like this:
stringA = #"29.88";
stringB = #"2564";
stringC = #"12";
stringD = #"-2";
what is the best way to convert them so they can all be used in the same mathmatical formula?? that includes add, subtract.multiply,divide etc
Probably floatValue (as it appears you want floating-point values), though integerValue may also be of use (both are instance methods of NSString).
[stringA doubleValue]
These are all wrong, because they don't handle errors well. You really want an NSNumberFormatter.
If you have the string #"abc" and try to use intValue or floatValue on it, you'll get 0.0, which is obviously incorrect. If you parse it with an NSNumberFormatter, you'll get nil, which is very easy to distinguish from an NSNumber (which is what would be returned if it was able to parse a number).
Assuming that you have NSString variables.
NSString *stringA = #"29.88";
NSString *stringB = #"2564";
NSString *stringC = #"12";
NSString *stringD = #"-2";
suppose, you want to convert a string value to float value, use following statement.
float x=[stringA floatValue];
suppose, you want to convert a string value to integer value, use following statement.
NSInteger y = [stringC intValue];
Hope, it helps to you.