How to convert a string into double and vice versa

Question

I want to convert a string into a double and after doing some math on it  convert it back to a string   How do I do this in Objective-C   Is there a way to round a double to the nearest integer too

User · Accepted Answer

You can convert an NSString into a double with

double myDouble = [myString doubleValue];

Rounding to the nearest int can then be done as

int myInt = (int)(myDouble + (myDouble>0 ? 0.5 : -0.5))

I'm honestly not sure if there's a more streamlined way to convert back into a string than

NSString* myNewString = [NSString stringWithFormat:@"%d", myInt];

User · Answer

To really convert from a string to a number properly  you need to use an instance of NSNumberFormatter configured for the locale from which you re reading the string   Different locales will format numbers differently   For example  in some parts of the world  COMMA is used as a decimal separator while in others it is PERIOD      and the thousands separator  when used  is reversed   Except when it s a space   Or not present at all   It really depends on the provenance of the input   The safest thing to do is configure an NSNumberFormatter for the way your input is formatted and use - NSFormatter numberFromString   to get an NSNumber from it   If you want to handle conversion errors  you can use - NSFormatter getObjectValue forString range error   instead

User · Answer

convert text entered in textfield to integer  double mydouble   myTextfield text doubleValue     rounding to the nearest double  mydouble  round mydouble      rounding to the nearest int considering only positive values   int myint  int  mydouble     converting from double to string  myLabel text  NSString stringWithFormat    f  mydouble     or  NSString  mystring  NSString stringWithFormat    f  mydouble     converting from int to string  myLabel text  NSString stringWithFormat    d  myint     or  NSString  mystring  NSString stringWithFormat    f  mydouble

User · Answer

For conversion from a number to a string  how about using the new literals syntax  XCode    4 4   its a little more compact   int myInt    int round     1 6  floatValue      NSString  myString      myInt  description      Boxes it up as a NSNumber and converts to a string using the NSObjects  description method

User · Answer

Adding to olliej s answer  you can convert from an int  back to a string with NSNumber s stringValue     NSNumber numberWithInt myInt  stringValue    stringValue on an NSNumber invokes descriptionWithLocale nil  giving you a localized string representation of value  I m not sure if  NSString stringWithFormat    d  myInt  will give you a properly localized reprsentation of myInt

User · Answer

Converting String in to Double  double doubleValue    yourString doubleValue       Converting Double in to String NSString  yourString    NSString stringWithFormat     20f   doubleValue       20f takes the value up to 20 position after decimal     Converting double to int  int intValue    int  doubleValue  or int intValue    yourString intValue

User · Answer

To really convert from a string to a number properly  you need to use an instance of NSNumberFormatter configured for the locale from which you re reading the string   Different locales will format numbers differently   For example  in some parts of the world  COMMA is used as a decimal separator while in others it is PERIOD      and the thousands separator  when used  is reversed   Except when it s a space   Or not present at all   It really depends on the provenance of the input   The safest thing to do is configure an NSNumberFormatter for the way your input is formatted and use - NSFormatter numberFromString   to get an NSNumber from it   If you want to handle conversion errors  you can use - NSFormatter getObjectValue forString range error   instead

User · Answer

Here s a working sample of NSNumberFormatter reading localized number String  xCode 3 2 4  osX 10 6   to save others the hours I ve just spent messing around  Beware  while it can handle trailing blanks such as  8 765 4    this cannot handle leading white space and this cannot handle stray text characters   Bad input strings    8  and  8q  and  8 q     NSString  tempStr     8 765 4             localization allows other thousands separators  also  NSNumberFormatter   myNumFormatter     NSNumberFormatter alloc  init    myNumFormatter setLocale  NSLocale currentLocale       happen by default   myNumFormatter setFormatterBehavior NSNumberFormatterBehavior10 4           next line is very important   myNumFormatter setNumberStyle NSNumberFormatterDecimalStyle      crucial  NSNumber  tempNum    myNumFormatter numberFromString tempStr   NSLog   string      gives NSNumber      with intValue   i         tempStr  tempNum   tempNum intValue     myNumFormatter release       good citizen

User · Answer

This is the easiest way I know of   float myFloat   5 3  NSInteger myInt    NSInteger myFloat

User · Answer

For rounding  you should probably use the C functions defined in math h   int roundedX   round x     Hold down Option and double click on round in Xcode and it will show you the man page with various functions for rounding different types

User · Answer

from this example here  you can see the the conversions both ways   NSString  str   5678901234567890    long long verylong  NSRange range  range length   15  range location   0     NSScanner scannerWithString  str substringWithRange range   scanLongLong  amp verylong    NSLog   long long value  lld  verylong

User · Answer

Adding to olliej s answer  you can convert from an int  back to a string with NSNumber s stringValue     NSNumber numberWithInt myInt  stringValue    stringValue on an NSNumber invokes descriptionWithLocale nil  giving you a localized string representation of value  I m not sure if  NSString stringWithFormat    d  myInt  will give you a properly localized reprsentation of myInt

User · Answer

For rounding  you should probably use the C functions defined in math h   int roundedX   round x     Hold down Option and double click on round in Xcode and it will show you the man page with various functions for rounding different types

User · Answer

olliej s rounding method is wrong for negative numbers   2 4 rounded is 2  olliej s method gets this right  -2 4 rounded is -2  olliej s method returns -1    Here s an alternative     int myInt    int  myDouble    myDouble gt 0   0 5   -0 5     You could of course use a rounding function from math h

User · Answer

I ended up using this handy macro    define STRING value                   value  stringValue

[objective-c] How to convert a string into double and vice versa?

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