// NSString

        //代开API文档

        //Xcode -> help - Documentation and API Reference

    

        //快速打开API

        //alt(option) + 鼠标左键

    

        //快速进入头文件

        //command + 鼠标左键

    

//        NSString是oc中的不可变字符串类,被创建后,不能修改

    

        //常用方法

        //1.创建字符串

    NSString *str1 = @"iPhone";

    NSLog(@"%@", str1);

    NSString *str2 = [[NSString alloc] init];

    NSLog(@"%@", str2);

    NSString *str3 = [[NSString alloc] initWithString:@"iPhone"];

    NSLog(@"%@", str3);

//    NSString *str4 = [[NSString alloc] initWithString:nil];

//    NSLog(@"%@", str4);  error

    NSString *str5 = [[NSString alloc] initWithFormat:@"%@5s", str1];

    NSLog(@"%@", str5);

    

//    NSString *str6 = [NSString stringWithString:@"iPhone"];

//    NSLog(@"%@", str6);

    NSString *str7 = [NSString stringWithFormat:@"123"];

    NSLog(@"%@", str7);

        //2.获取字符串长度

    NSUInteger length = [str7 length];

    NSLog(@"%lu", length);

    

        //3.判断字符串是否以指定字符串开始或结束

    NSString *str8 = @"123ABC";

    

   BOOL result = [str8 hasPrefix:@"223"];

    NSLog(@"%d", result);

    BOOL result1 = [str8 hasSuffix:@"C"];

    NSLog(@"%d", result1);

    

        //4.搜索字符串的范围

    

    NSRange range = [str8 rangeOfString:@"3A"];

    

    NSLog(@"%lu, %lu", range.length, range.location);

    

        //5.字符串截取

    NSRange rs = {

3, 3};

    NSString *str9 = [str8 substringWithRange:rs];

    NSLog(@"%@", str9);

        //6.拼接字符串

   NSString *str10 = [str8 stringByAppendingString:@"123"];

    NSLog(@"%@", str8);

    NSLog(@"%@", str10);

        //7.替换字符串

   NSString *str11 = [str8 stringByReplacingOccurrencesOfString:@"3A" withString:@"A"];

    NSLog(@"%@", str11);

    

        //8.字符串比较"123" "123" "321"

    

    NSInteger flag = [@"123" compare:@"123"];

    NSLog(@"%ld", flag);

    

        //9.字符串和数值类型的转换

    NSString *str12 = @"123";

    int a = [str12 intValue];

    NSLog(@"%d", a);

    double b = [str12 doubleValue];

    NSLog(@"%f", b);

    float c = [str12 floatValue];

    NSLog(@"%f", c);

    BOOL e = [str12 boolValue];

    NSLog(@"%d", e);

//10.大小写转换操作

    NSString *aaa = @"aBcE";

    NSLog(@"%@", [aaa capitalizedString]);

    NSLog(@"%@", [aaa uppercaseString]);

    NSLog(@"%@", [aaa lowercaseString]);

    NSLog(@"%@", aaa);

    

    

        //NSMutableString

        //capctiy 是一个预估的值,可以改变

        //由于内存比较紧张,一般把capctiy设置成0,让字符串自己去判断大小,扩充容器大小

        //创建一个新的字符串

    NSMutableString *mString = [[NSMutableString alloc] initWithCapacity:0];

        //拼接字符串

    [mString appendString:@"taiyang"];

    NSLog(@"%@", mString);

    

         //插入字符

    [mString insertString:@"aaa" atIndex:1];

    NSLog(@"%@", mString);

    

        //删除字符串

//    NSRange r = {2, 3};

//    [mString deleteCharactersInRange:r];

//             ||  等价

    [mString deleteCharactersInRange

 

练习 :   

 

//    1.截取字符串“20|”中 “|” 前面和后面的字符串，并输出。

//    NSString *str1 = @"20|";

//         1

//    NSString *str2 = [str1 substringWithRange:NSMakeRange(0, 2)];

//    NSString *str3 = [str1 substringWithRange:NSMakeRange(3, 20)];

//    NSLog(@"str2 = %@ str3 = %@", str2, str3);

        //2

//    NSString *str2 = [str1 substringFromIndex:3];

//    NSLog(@"str2 = '%@'", str2);

//    NSString *str3 = [str1 substringToIndex:2];

//    NSLog(@"str3 = '%@'", str3);

 

//    2.将“文艺青年”改成“213青年”。

    

//    NSString *str1 = @"文艺青年";

//    NSString *str2 = [str1 stringByReplacingOccurrencesOfString:@"文艺" withString:@"213"];

//    NSLog(@"%@", str2);

        //    3.给定一个图片文件名，判断字符串中是否有后缀,如果有(如:以“.png”结尾)，就替换成“jpg”;如果没有，就拼接”.jpg”

    

    

//    NSString *str1 = @"taiyang";

//    NSUInteger length = [str1 length];

//    NSString *str2 = [str1 substringFromIndex:length - 4];

//    if ([@".jpg" compare:str2] == 0) {

//        NSLog(@"该字符串是以.jpg开头");

//    }else if ([@".png" compare:str2] == 0){

//        NSString *str3 = [str1 stringByReplacingOccurrencesOfString:@".png" withString:@".jpg"];

//        NSLog(@"str3 = '%@'", str3);

//    }else{

//        NSString *str4 = [str1 stringByAppendingString:@".jpg"];

//        NSLog(@"str4 = '%@'", str4);

//    }