Trying to put user input in yahoo api URL

Trying to put user input in yahoo api URL

I am trying to learn ios and my first project is to make an app that
displays weather forecast in the area the of the zip code the user enters.
I have the url which is:
NSString *zipUrl =
@"http://query.yahooapis.com/v1/public/yql?q=select%20item%20from%20weather.forecast%20where%20location%3D%2289448%22&format=json";
The zip code is near the end after 3D%22:
3D%22*89448*%22
I just need to figure out how to insert what the user entered in a text
box into this spot. I have tried [NSString StringWithFormat] but there are
to many % signs that it doesn't work.
Please let me know if you need any more info.