//创建oc常量字符串

        NSString *str=@"hello world!";

        NSLog(@"%@",str);

        //用c语言的字符串来创建oc的字符串

        char *ch="hello world C";

        NSString *str2=[[NSString alloc] initWithUTF8String:ch];

        NSLog(@"%@",str2);

        //用格式化来创建字符串

        int a=;

        NSString *str3=[[NSString alloc] initWithFormat:@"%@ %d",str2,a];

        NSLog(@"%@",str3);

        //用类方法来创建字符串

        NSString *str4=[NSString stringWithFormat:@"%@%@",str2,str];

        NSString *str5=[NSString stringWithUTF8String:ch];

        NSLog(@"%@ , %@",str4,str5);

        //读取文件来创建字符串

        NSString *path=@"/Users/qf/Desktop/my2/Car.h";

        NSError *error;

        NSString *str6=[[NSString alloc] initWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&error];

        NSLog(@"%@",str6);

        NSString *str1=@"hello world";

        NSString *str2=@"Hello world";

        if([str1 isEqualToString:str2])

        {

            NSLog(@"yes");

        }

        else

        {

            NSLog(@"no");

        }

        if ([str1 compare:str2]==-) {

            NSLog(@"str1<str2");

        }

        else if ([str1 compare:str2]==)

        {

            NSLog(@"str1==str2");

        }

        else

        {

            NSLog(@"str1>str2");

        }
    

        //不区分大小写

        if ([str1 caseInsensitiveCompare:str2]==-) {

            NSLog(@"str1<str2");

        }

        else if ([str1 caseInsensitiveCompare:str2]==)

        {

            NSLog(@"str1==str2");

        }

        else

        {

            NSLog(@"str1>str2");

        }
        

        //转大写

        NSString *str3=[str1 uppercaseString];

        NSLog(@"%@",str3);

        //转小写

        NSString *str4=[str2 lowercaseString];

        NSLog(@"%@",str4);

        //首字母大写，其他变小写

        NSString *str5=[str2 capitalizedString];

        NSLog(@"%@",str5);
    

        //查找是否包含

        NSString *str6=@"I love huang xiao dan.";

        NSString *str7=@"love";

        NSRange range=[str6 rangeOfString:str7];

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

        if (range.location==NSNotFound) {

            NSLog(@"没找到");

        }

        else

        {

            NSLog(@"找到了");

        }

        //查找某个位置的字符

        char c=[str6 characterAtIndex:];

        NSLog(@"%c",c);

        //从位置0开始，截取到指定的位置，开区间

        NSString *str8=[ str6 substringToIndex:];

        NSLog(@"%@",str8);

        //从指定的位置开始，一直截取到字符串的末尾，闭区间

        NSString *str9=[str6 substringFromIndex:];

                   NSLog(@"%@",str9);

        //截取指定范围的字符串

        NSRange range1=NSMakeRange(, );

        NSString *str10=[str6 substringWithRange:range1];

        NSLog(@"%@",str10);

         //判断字符串是否以“I”开头

         if([str6 hasPrefix:@"I"])

        {

            NSLog(@"yes");

        }

        else

        {

            NSLog(@"no");

        }

        //判断字符串是否以“dan”结尾

        if([str6 hasSuffix:@"dan"])

        {

            NSLog(@"yes");

        }

        else

        {

            NSLog(@"no");

        }
    

        NSString *str11=@"";

        NSLog(@"%d",[str11 intValue]);

        //转其他数字类型类似

        NSString *str12=@"I am a good student.";

        NSString *str13=[str12 stringByReplacingCharactersInRange:NSMakeRange(, ) withString:@"asjhja"];

        NSLog(@"%@",str13);    

        //单个字符分割

        NSArray *array=[str12 componentsSeparatedByString:@" "];

        NSLog(@"%@",array);

        //字符集进行分割

        NSString *str14=@"I like a cat,and!dn sa!";

        NSCharacterSet *set=[NSCharacterSet characterSetWithCharactersInString:@" , !"];

        NSArray *array2=[str14 componentsSeparatedByCharactersInSet:set];

        NSLog(@"%@",array2);

        //字符组合

        NSString *str15=[array2 componentsJoinedByString:@"!"];

        NSLog(@"%@",str15);