pascal括号匹配检查的程序,用栈的（最好有解释）

program bracket;const a:array['a'。。'd']of byte=(1,2,3,0);var n,t,i,j:longint; p:boolean; s:string; c:array[0。。255]of char;procedure pop;begin dec(t);end;procedure push(x:char);begin inc(t); c[t]:=x;end;begin readln(n); for i:=1 to n do begin readln(s); c[0]:='d'; t:=0; p:=true; for j:=1 to length(s) do case s[j] of '{':s[j]:='a'; '[':s[j]:='b'; '(':s[j]:='c'; end; while length(s)0 do begin case s[1] of '}':if c[t]='a' then pop else begin p:=false; break; end; ']':if c[t]='b' then pop else begin p:=false; break; end; ')':if c[t]='c' then pop else begin p:=false; break; end; else if a[c[t]]