add calc prefix
rebuild expression
try to create a stack easy
finish new stack
finish new stack
use new stack finish post_eval
add Makefile
finish in2post use struct stack
finish in2pre in2post without paren
change in2pre use one loop
fix a bug of lparen and rparen
finish post2in
finish get_operands
finish post2in
change nothing
Merge branch 'master' of https://github.com/mycmessia/DSinC
merge my blog.