Question

Not sure why one snippet works while the other fails:

This fails(the app quits) after pressing the button 3 times (this code snipped is executed on a “button press”):

sUser = [NSString stringWithFormat: @"%@ %c", sUser, charcode];//appendstring

Note: that in the header file sUser is defined as NSString and charcode is an int;

This works (this code snippet is executes on a “button press”):

int r;
theString = @"";

for(i = 0; i < iDigits ; i++)
{
    r = rand() % 26;
    theString = [NSString stringWithFormat: @"%@ %c", theString, r + 65];//appendstring
}

Note: that in the header file theString is defined as NSString;

Answer 1

The reason for the crash is if sUser is defined in the header this means that it belongs to your class and needs to be assigned to a retained string. If you have a property for sUser do this

self.sUser = [NSString stringWithFormat: @"%@ %c", sUser?:@"", charcode];

otherwise

NSString *temp = [NSString stringWithFormat: @"%@ %c", sUser?:@"", charcode];
[sUser release];
sUser = [temp retain];

Now there is a better more efficient way for appending strings NSMutableString.