NSString *str1 = @"BeiJing";
NSString *str2 = @"beijing";

//全部转为大写  
NSLog(@"%@",[str1 uppercaseString]);  

//全部转为小写  
NSLog(@"%@",[str1 lowercaseString]);  
 
//首字母大写  
NSLog(@"%@",[str1 capitalizedString]);  
 
//比较两个字符串内容是否相同  
BOOL b =[str1 isEqualToString:str2];  
 
//两个字符串内容比较  
//NSOrderedAscending    右边 > 左边  
//NSOrderedSame         内容相同  
//NSOrderedDescending   左边 > 右边  
NSComparisonResult result = [str1 compare:str2];  
if (result == NSOrderedAscending) {  
   NSLog(@"右边 > 左边");  
}else if(result == NSOrderedSame){  
   NSLog(@"内容相同");  
}else if (result == NSOrderedDescending){  
   NSLog(@"左边 > 右边");  
}  
 
//忽略大小写进行比较，返回值与compare一样  
result = [str1 caseInsensitiveCompare:str2];  
if (result == NSOrderedAscending) {  
   NSLog(@"右边 > 左边");  
}else if(result == NSOrderedSame){  
   NSLog(@"内容相同");  
}else if (result == NSOrderedDescending){  
   NSLog(@"左边 > 右边");  
}  
 
//判断字符串是否以指定字符串开头  
[str1 hasPrefix:@"aaa"];  
//判断字符串是否以指定字符串结尾  
[str1 hasSuffix:@"aaa"];  
 
//判断字符串是否包含指定字符串，返回位置和长度  
NSRange range = [@"123456" rangeOfString:@"456"];  
NSLog(@"%@", NSStringFromRange(range));  
 
//反向搜索  
range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch];  
NSLog(@"%@",NSStringFromRange(range));  
 
//指定范围进行搜索  
range = NSMakeRange(0, 9);  
range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch range:range];  
NSLog(@"%@",NSStringFromRange(range));  

    //字符串的截取  
    NSString *str = @"123456789";  
    NSLog(@"%@",[str substringFromIndex:3]);  
    NSLog(@"%@",[str substringToIndex:6]);  
    NSLog(@"%@",[str substringWithRange:NSMakeRange(3, 3)]);  
      
    //用指定字符串分割字符串，返回一个数组  
    NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];  
    NSLog(@"%@",array);  
      
    //将数组中的字符串组合成一个文件路径  
    NSMutableArray *components = [NSMutableArray array];  
    [components addObject:@"Users"];  
    [components addObject:@"CentralPerk"];  
    [components addObject:@"Desktop"];  
    NSString *path = [NSString pathWithComponents:components];  
    NSLog(@"%@",path);  //Users/CentralPerk/Desktop  
      
    //将一个路径分割成一个数组  
    NSArray *array1 = [path pathComponents];  
    NSLog(@"%@",array1);  
      
    //判断是否为绝对路径(依据：是否以'/'开始)  
    path = @"/Users/CentralPerk/Desktop";  
    NSLog(@"%i",[path isAbsolutePath]);  
      
    //获取最后一个目录  
    NSLog(@"%@",[path lastPathComponent]);  
      
    //删除最后一个目录  
    NSLog(@"%@",[path stringByDeletingLastPathComponent]);  
      
    //拼接一个目录  
    NSLog(@"%@",[path stringByAppendingPathComponent:@"aaa"]);   ///Users/CentralPerk/Desktop/aaa  
    NSLog(@"%@",[path stringByAppendingString:@"aaa"]);      ///Users/CentralPerk/Desktopaaa  
    NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);  ///Users/CentralPerk/Desktopbc  
      
    //拓展名出来  
    //获取拓展名,不带.  
    NSString *str2 = @"Users/CentralPerk/Desktop/test.txt";  
    NSLog(@"%@",[str2 pathExtension]);  
    //添加拓展名,不需要带.  
    NSLog(@"%@",[str2 stringByAppendingPathExtension:@"mp3"]);  
    //删除拓展名,带.一块删除  
    NSLog(@"%@",[str2 stringByDeletingPathExtension]);  
      
    //字符串转为 int double float  
    NSString *str3 = @"123";  
    NSLog(@"%i",[str3 intValue]);  
    NSLog(@"%zi",[str3 length]);  
      
    //取出指定位置的字符  
    unichar c = [str3 characterAtIndex:2];  
    NSLog(@"%c",c);  
      
    //转为C语言的字符串  
    const char *s = [str3 UTF8String];  
    NSLog(@"%s",s);