Question

How to multiply two text field float values and automatically update it in the third one in iphone?

I am getting warning: local declaration of ‘distance’ hides instance variables
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-(void)textFieldDidEndEditing:(UITextField *)textField{
    double distance = [self.distance.text doubleValue];
    double mileage = [self.mileagerate.text doubleValue];
     amount.text =  [NSString stringWithFormat:@"%.2f",distance * mileage];
}

Answer 1

The warning is because you have a text field named distance an a local variable also named distance. Rename your local variable and the warning should go away:

-(void)textFieldDidEndEditing:(UITextField *)textField{
    double dist = [self.distance.text doubleValue];
    double mileage = [self.mileagerate.text doubleValue];
     amount.text =  [NSString stringWithFormat:@"%.2f",dist * mileage];
}