void ex1()

 {

     //1.常量字符串的对象

     NSString *str1 = @"hello world";

     NSLog(@"str1 = %@",str1);

     //2.通过类方法创建字符串

     NSString *str2 = [NSString stringWithString:str1];

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

     //3.通过实例方法创建

     NSString *str3 = [[NSString alloc]initWithString:str1];

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

     //4.格式化字符串方式创建

     NSString *str4 = [NSString stringWithFormat:@"name=%@,password=%@",@"admin",@""];

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

     //5.通过C语言字符串的创建

     char *pstr = "how are you?";

     NSString *str5 = [NSString stringWithUTF8String:pstr];

     NSLog(@"str5 = %@",str5);

     //6.通过文件的方式创建字符串

     NSError *error = nil;

     NSUInteger enc;

     NSString *str6 = [[NSString alloc]initWithContentsOfFile:@"/Users/mac/Java/IO/2.txt" usedEncoding:&enc error: &error];

     if(!error)

     {

         NSLog(@"str6 = %@",str6);

     }

     else

     {

         NSLog(@"读取文件失败:%@",error);

     }

     //7.通过网络数据创建字符串

     NSURL *url = [NSURL URLWithString:@"http://www.baidu.com"];

     NSString *str7 = [NSString stringWithContentsOfURL:url encoding:NSUTF8StringEncoding error:&error];

     if(!error)

     {

         NSLog(@"str7 = %@",str7);

     }

     else

     {

         NSLog(@"读取网络失败:%@",error);

     }

 }

 void ex2()

 {

     //1.搜索字符串

     NSString *str = @"this is a test";

     NSRange nsr = [str rangeOfString:@"test"];//返回一个结构体

     if(nsr.length != )//找到字符串

     {

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

     }

     //2.查找字符串是不是以什么前缀开始

     NSString *str2 = @"http://www.sina.com.cn";

     if([str2 hasPrefix:@"http"])

     {

         NSLog(@"http协议");

     }

     //3.查找字符串是不是以什么后缀开始

     NSString *str3 = @"1.txt";

     if([str3 hasSuffix:@"txt"])

     {

         NSLog(@"文本文件");

     }

     //4.在字符串中截取字串

     NSString *str4 = @"http://www.sxt.cn?user=admin&password=1233456";

     NSRange range1 = [str4 rangeOfString:@"user="];

     NSRange range2 = [str4 rangeOfString:@"&password="];

     //求出user的字符串区间并输出字符串

       //用户名起始位置

     NSUInteger location = range1.location + range1.length;

       //用户名的有效长度

     NSUInteger length = range2.location - location;

     NSRange range3 = NSMakeRange(location,length);

     NSString *user = [str4 substringWithRange:range3];

     //求出password的字符串

     NSString *password = [str4 substringFromIndex:range2.location+range2.length];

     NSLog(@"user=%@,password=%@",user,password);

 }

 void ex3()

 {

     //对象比较

     //1.判断两个对象是不是同一个对象

     NSString *str1 = @"hello world";

     NSString *str2 = @"how are you";

     NSString *str3 = str1;

     if(str1 == str3)

     {

         NSLog(@"str1和str3是同一个对象");

     }

     //或者

     if([str1 isEqual:str3])

     {

         NSLog(@"str1和str3是同一个对象");

     }

     //或者

     if([str1 isEqualTo:str3])

     {

         NSLog(@"str1和str3是同一个对象");

     }

     //2.判断字符串是否相等

     if([str1 isEqualToString:@"hello world"])

     {

         NSLog(@"字符串相等");

     }

     //3.字符串的比较

     NSComparisonResult result = [str1 compare:str2];

     if(result== NSOrderedSame)

     {

         NSLog(@"两个字符串相等");

     }

     else if(result == NSOrderedAscending)

     {

         NSLog(@"第一个小于第二个字符串");

     }

     else

     {

         NSLog(@"第一个大于第二个字符串");

     }

 }

 void ex4()

 {

     //1.其它类型转换成字符串

     NSString *str1 = [NSString stringWithFormat:@"%D,%.2f,%c,%s",,12.34,'A',"hello world"];

     NSLog(@"str1 = %@",str1);

     //2.字符串转换为整型

     NSString *str2 = @"";

     NSInteger  i = [str2 integerValue];

     NSLog(@"i = %ld",i);

     //3.字符串转换为实型

     NSString *str3 = @"12.34";

     CGFloat f = [str3 doubleValue];

     NSLog(@"f = %.2f",f);

     //4.字符串转换为C语言的字符串

     NSString *str4 = @"how are you";

     const char *pstr = [str4 UTF8String];

     NSLog(@"pstr = %s",pstr);

 }