复杂计算(Complex Calculation)

 我有一段时间让这段代码正确地摆脱出来。 我目前卡在最后一行文字中。 我是新手一起编写代码。 我所学到的一切都是通过网站和网站找到的。 请参阅下面带下划线的注释。 请帮助，以便我可以看到我的计算是否有效...... 
 
//.h


@interface ViewController : UIViewController

@property (weak, nonatomic) IBOutlet UITextField *Price87;
@property (weak, nonatomic) IBOutlet UITextField *MPG87;
@property (weak, nonatomic) IBOutlet UITextField *PriceE85;
@property (weak, nonatomic) IBOutlet UITextField *MPGE85;
@property (weak, nonatomic) IBOutlet UITextField *GasTankSize;

- (IBAction)Settings:(id)sender;
- (IBAction)pergallon:(id)sender;
- (IBAction)pertank:(id)sender;

@end


//.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController   <-----------  Getting a Incomplete Implementation here...

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)Settings:(id)sender {
    Settings *settings = [[Settings alloc] initWithNibName:nil bundle:nil];
    [self presentViewController:settings animated:YES completion:NULL];
}

- (IBAction)addNums:(id)sender {
    int a = ([_Price87.text floatValue]);
    int b = ([_MPG87.text floatValue]);
    int c = ([_PriceE85.text floatValue]);
    int d = ([_MPGE85.text floatValue]);
    int e = ([_GasTankSize.text floatValue]);
    int ans = ((a*e)-((e+(a*e)-(c*e)/b)*d)/e);

    [ans setText:[NSString stringWithFormat:@"%i", pergallon]];   <---------  This is the line giving me trouble.  I'm getting a "use of undeclaired identifier 'pergallon'

}

@end

I'm having a heck of a time getting this code to shake out correctly. I'm currently stuck at the very last line of text. I'm new to writing code all together. Everything I've learned has been found online and through this site. Please see the underlined notes below. Please help so i can see if my calculation even works... 
 
//.h


@interface ViewController : UIViewController

@property (weak, nonatomic) IBOutlet UITextField *Price87;
@property (weak, nonatomic) IBOutlet UITextField *MPG87;
@property (weak, nonatomic) IBOutlet UITextField *PriceE85;
@property (weak, nonatomic) IBOutlet UITextField *MPGE85;
@property (weak, nonatomic) IBOutlet UITextField *GasTankSize;

- (IBAction)Settings:(id)sender;
- (IBAction)pergallon:(id)sender;
- (IBAction)pertank:(id)sender;

@end


//.m

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController   <-----------  Getting a Incomplete Implementation here...

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)Settings:(id)sender {
    Settings *settings = [[Settings alloc] initWithNibName:nil bundle:nil];
    [self presentViewController:settings animated:YES completion:NULL];
}

- (IBAction)addNums:(id)sender {
    int a = ([_Price87.text floatValue]);
    int b = ([_MPG87.text floatValue]);
    int c = ([_PriceE85.text floatValue]);
    int d = ([_MPGE85.text floatValue]);
    int e = ([_GasTankSize.text floatValue]);
    int ans = ((a*e)-((e+(a*e)-(c*e)/b)*d)/e);

    [ans setText:[NSString stringWithFormat:@"%i", pergallon]];   <---------  This is the line giving me trouble.  I'm getting a "use of undeclaired identifier 'pergallon'

}

@end

原文：https://stackoverflow.com/questions/17416598