//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=10;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]==-1) {NSLog(@"str1<str2");}else if ([str1 compare:str2]==0){NSLog(@"str1==str2");}else{NSLog(@"str1>str2");}

        //不区分大小写if ([str1 caseInsensitiveCompare:str2]==-1) {NSLog(@"str1<str2");}else if ([str1 caseInsensitiveCompare:str2]==0){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:7];NSLog(@"%c",c);

        //从位置0开始，截取到指定的位置，开区间NSString *str8=[ str6 substringToIndex:6];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:6];NSLog(@"%@",str9);//截取指定范围的字符串NSRange range1=NSMakeRange(3, 5);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=@"10";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(2, 3) 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);