How to copy from NSMutableArray to NSMutableString? - objective-c

Question

Im trying to add some strings into NSMutableArray,than want to copy element 0(zero)
from NSMutableArray to NSMutableString
[MS appendString:str]
this line raises error.
what is the problem ?
a MutableArray element cannot be assigned to NSString ?
(thanks for any responses)
error output is :
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber length]: unrecognized selector sent to instance 0x6c82440'
here is my code :
NSMutableArray *A=[[NSMutableArray alloc]init];
NSMutableString *MS=[NSMutableString stringWithString:#"first"];
for (int i=0; i<=15;i+=2) {
[A addObject:[NSNumber numberWithInteger:i]];
}
NSString *str;
for (int x=0; x<[A count]; x++) {
str=[A objectAtIndex:0];
[MS appendString:str];//ERROR HERE
}
[A release];

Answer 1

You are adding NSNumbers to the array and not strings n the folioing line:
[A addObject:[NSNumber numberWithInteger:i]]; // here you are adding numbers
So when you read them from the array later, they are still numbers and you have to create strings from them:
NSString *str;
NSNumber *number;
for (int x=0; x<[A count]; x++) {
number = [A objectAtIndex:0]; // You should probably replace 0 by x here.
str = [number stringValue]; // transform number into a string
[MS appendString:str];
}
[A release];
But if you want the array to store strings and not numbers, then replace the first loop instead with the following:
for (int i=0; i<=15;i+=2) {
[A addObject:[[NSNumber numberWithInteger:i] stringValue]];
}
Or
for (int i=0; i<=15;i+=2) {
[A addObject:[NSString stringWithFormat:#"%d", i]];
}