Question

I am doing the comparison:

 else if([change doubleValue] == 0 && indexPath.row == sectionRows - 1)

how can I check for the case where [change doubleValue] doesn’t return anything?

Answer 1

There’s no way the doubleValue method goes without returning anything. The least value you can check for is 0. The following are the cases the doubleValue returns 0.

1. The string doesn’t contain a valid numerical value.
2. The string is nil.
3. The string actually contains @"0".

Checking for a valid number
Use NSPredicate to test if the string contains a numerical value.

NSString *str = @"sfas";
NSString *regx = @"(-){0,1}(([0-9]+)(.)){0,1}([0-9]+)";
NSPredicate *test = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", regx];
BOOL isAValidNumber = [test evaluateWithObject:str];