swift版本:

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textFields1: UITextField!
    
    @IBOutlet weak var textFields2: UITextField!
    
    @IBOutlet weak var resultLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    
    @IBAction func clickBtn(_ sender: UIButton) {
        
这种方法可行
//        let str1 : NSInteger = (Int)(self.textFields1.text!)!
//        let str2 : NSInteger = (Int)(self.textFields2.text!)!
        
        第二种方法:
        let str3 : NSInteger = (self.textFields1.text as NSString).integerValue
        let str4 : NSInteger = (self.textFields2.text! as NSString).integerValue
        //str3报错误:  Cannot convert value of type 'String?' to type 'NSString' in coercion(强制)

        self.resultLabel.text = String.init(format: "%zd", (str1 + str2)
        
        )
        
    }
    

oc版本:

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UITextField *textField1;

@property (weak, nonatomic) IBOutlet UITextField *textFiled2;
@property (weak, nonatomic) IBOutlet UILabel *resultLabel;

@end


@implementation ViewController

- (IBAction)btn:(id)sender {
    
    NSLog(@"aaa");
    
    NSString *str1 = self.textField1.text;
    NSString *str2 = self.textFiled2.text;
    
    NSInteger num1 = str1.integerValue;
    NSInteger num2 = str2.integerValue;
    
    NSInteger result = num1 + num2;
    
//    self.resultLabel.text = @(result).description;
    self.resultLabel.text = [NSString stringWithFormat:@"%zd",result];
    
    
}