Why is NSSArray not populating when parsing JSONArray? - iphone

Question

I'm a noob to iphone development and I'm trying to parse the JSONArray from this link. The problem is that when this code is executed it returns that my NSArray contains only 4 values instead of 80 values that jSONArray at the link contains. Am I properly converting the NSDictionary into NSArray. Any help is greatly appreciated. I'm following this tutorial here.
//parse out the json data
NSError* error;
NSDictionary* json = [NSJSONSerialization JSONObjectWithData:responseData //1
options:kNilOptions
error:&error];
NSArray* bitcoin = json; //2
NSLog(#"size of bitcoin is %lu", sizeof(bitcoin));
// 1) Get the bitcoin rate mtgoxUSD
for(int i = 0; i < sizeof(bitcoin); i++){
NSDictionary* forex = [bitcoin objectAtIndex:i];
NSString *mtgoxUSD = [forex objectForKey:#"symbol"];
NSLog(#"value against mtgoxUSD %#", mtgoxUSD);
if (mtgoxUSD==#"mtgoxUSD") {
NSString *bitcoinrate = [forex objectForKey:#"avg"];
if (bitcoinrate==#""||bitcoinrate==NULL) {
currencyBTC=1;
NSLog(#"currencyBTC: is 1");
}else{
currencyBTC=[bitcoinrate floatValue];
NSLog(#"currencyBTC: %f", currencyBTC);
}
break;
}
}

Answer 1

sizeof will return the size of the pointer structure in bytes, that's why you always see 4 as the value.
You should use the count method instead:
for(int i = 0; i < [bitcoin count]; i++)

Answer 2

"Am I properly converting the NSDictionary into NSArray"
No, not quite! JSONObjectWithData can return an array or a dictionary, depending on the JSON you're parsing. In this case, your JSON has a top-level array, so you don't need to convert it at all.
So first of all, replace your first few lines with this:
NSArray* json = [NSJSONSerialization JSONObjectWithData:responseData //1
options:kNilOptions
error:&error];
You then want to iterate through your array, but your current iteration code isn't quite right. You can use the count method that pgb suggested in another answer, or alternatively you can use the really nifty 'fast enumeration' feature of Objective-C, which looks like this:
for id item in json {
// Will iterate through all objects in the json array, accessible via item
}