Wrong conversion from number to string

How can I convert a number into string.

Here is my code:

NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:@"1100", @"myKey",nil];
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NSString *myData = [NSString stringWithFormat:@"%d", [myDict valueForKey:@"myKey"]];

The output in myData is not 1100 but some random number. What is wrong here.

The number that you're storing already is in form of a string (note the quotes: @"…").

What you likely want is something like this:

NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithInteger:1100], @"myKey",nil];

NSString *myData = [NSString stringWithFormat:@"%d", [[myDict objectForKey:@"myKey"] integerValue]];

Let's go thru that code step by step:

1. We create an NSNumber object holding 1100 via [NSNumber numberWithInteger:1100]
2. We create an NSDictionary object with said number object as value for key @"myKey"
3. We request the value for key @"myKey" from myDict via [myDict objectForKey:@"myKey"], which will return the NSNumber instance that we had passed to it previously.
4. We then request the integer value (NSInteger, which is an abstraction around int/long) of the received NSNumber instance via [… integerValue]
5. We pass the NSInteger value to [NSString stringWithFormat:@"%d", …]

Alternatively you could skip step 4 and change @"%d" to @"%@", which will print the same. In case of simple integer values at least. For floating point values you would not want to print NSNumbers directly via @"%@" as you'd loose control over display of decimal precision.

Note that we use objectForKey:, not valueForKey:, here is why: https://stackoverflow.com/search?q=valueForKey%20objectForKey

You could have made the same string by changing your code to this:

NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:@"1100", @"myKey",nil];

NSString *myData = [NSString stringWithFormat:@"%@", [myDict objectForKey:@"myKey"]];

The reason though, why would not want to do this: It is (in general) bad practice to store numeric **(or just about any other non-textual) values as strings**.

%d is a specifier for integer values while you are inserting @"1100", which is a NSString, inside the dictionary.

Change the specifier with %@ and it will work.. or if you want to place the number itself you will have to wrap it with a Obj-C object (like NSNumber) inside the dictionary.

Both other answers are correct, but...

You appear to want:

NSDictionary *myDict = [NSDictionary dictionaryWithObjectsAndKeys:@"1100", @"myKey",nil];
NSString *myData = [myDict valueForKey:@"myKey"];

There's no need to do the +stringWithFormat: dance because you're already storing the value as a string (@"..." means that it's a string).