invalid char to char(pointer) conversion?

here is what i tried.

devcpp. winnapp.
Code:
  char    *buff;

 buff = (char*)GlobalAlloc( GPTR, textlen + 1);



   buff =   buff[strcspn ( buff, "\n" )] = '\0'; 

get error

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `char' to `char*' 

     buff =   GPTR buff[strcspn ( buff, "\n" )] = '\0'; 

get error

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `int' to `char*' 

     buff =   GPTR buff[strcspn ( GPTR buff, "\n" )] = '\0';

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `int' to `char*' 



  buff =    buff[strcspn ( GPTR buff, "\n" )] = '\0'; 

2668 C:\Dev-Cpp\Project6\main.c expected `)' before "buff" 



     buff =    buff[strcspn ( (GPTR) buff, "\n" )] = '\0';  

2668 C:\Dev-Cpp\Project6\main.c expected `)' before "buff" 


   buff =  (GPTR)  buff[strcspn ( (GPTR) buff, "\n" )] = '\0';

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `int' to `char*' 


     buff =    buff[strcspn ( (char *) buff, "\n" )] = '\0';  

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `char' to `char*' 


 buff =    buff[strcspn (  &buff, "\n" )] = '\0';  

2668 C:\Dev-Cpp\Project6\main.c cannot convert `char**' to `const char*' for argument `1' to `size_t strcspn(const char*, const char*)' 

    buff =    buff[strcspn (  buff, '\n' )] = '\0';  

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `char' to `const char*' 

  buff =    buff[strcspn (  buff, "\n" )] = "\0";  

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `const char*' to `char' 

 buff =    buff[strcspn (  buff, (char *) "\n" )] = '\0';

2668 C:\Dev-Cpp\Project6\main.c invalid conversion from `char' to `char*' 

and back to the origial 

 buff =    buff[strcspn (  buff,  "\n" )] = '\0'; 


  (char pointer ==> buff)  =  (char pointer ==> buff)[strcspn( (char pointer ==> buff) , (string ==> "\n" ) )] = ( char ==> '\0' ) ;

so....

  buff =    buff[strcspn (  buff,  "\n" )] = GPTR '\0';

after adding (char *) one at a time then compile each of the three

 buff =    (char *) buff[strcspn (  buff, (char *) "\n" )] = (char *) '\0'; 

get error

2668 C:\Dev-Cpp\Project6\main.c [Warning] cast to pointer from integer of different size 

<wimpers> arrrrgggghhhh! This prog needz a flee bath! </wimpers>