fix grammar

Author: vladak

intro.tex

@@ -1947,7 +1947,7 @@
 \item It is very reasonable to use only \texttt{EXIT\_SUCCESS} (\texttt{0}) and
 \texttt{EXIT\_FAILURE} (\texttt{1}) unless there is a valid reason for other
 values.  Sometimes you might need more values to distinguish between failures.
-For example, the \texttt{passwd} command on Solaris have quite a few of them, go
+For example, the \texttt{passwd} command on Solaris has quite a few of them, go
 check its manual page if interested, section \texttt{EXIT STATUS}.
 \item The difference between function \texttt{exit()} and \verb#_exit()# is that
 \texttt{exit} also flushes and closes streams (try it out with \texttt{printf()}