objective c - Implicit declaration of function "..." is invalid in C99? -

i'm trying declare function within function. here's part of code: viewcontroller.m

- (void)updatedisplay{     [_displaytext settext:[nsstring stringwithformat:@"%d", counter]];  }  - (ibaction)minus1:(id)sender {     counter--;     updatedisplay(); } 

viewcontroller.h

- (ibaction)minus1:(id)sender; - (void)updatedisplay; 

which returned me error of "implicit declaration of function "..." invalid in c99".

result: http://i.imgur.com/rsit6r2.png

i've found people have encountered similar problem, newbie didn't know next. help! :)

implicit declaration of function '...' invalid on c99

you not declaring function; instance method, call must send message self;

[self updatedisplay];

edit

as @rmaddy pointed out (thanks that) declared instance method not class method. make things clear;

- (return_type)instance_method_name.... called via 'self' or pointer object instance.
+ (return_type)class_method_name.... called directly on class (static).