C :

#include<stdio.h>
#include<stdlib.h>

typedef char ElemType;
typedef enum {TRUE,FALSE,OVERFLOW} Status;
#define MAXSIZE 200	//定义栈的最大容量
typedef struct
{
	ElemType elem[MAXSIZE];	//存放栈中元素的一维数组空间
	int top;			//栈顶指针变量
}SeqStack;

void InitStack (SeqStack *S)
{	//构造一个空栈S
	S -> top = 0;
}

Status StackEmpty (SeqStack *S)
{	//判断S是否为空栈，为空时返回TRUE，否则返回FALSE
	return (S->top == 0 ? TRUE : FALSE);
}

Status Push (SeqStack *S, ElemType e)
{	//将数据元素e压入栈顶
	if (S -> top == MAXSIZE)  return FALSE;//栈已满，进栈失败
	S -> elem[S -> top] = e;			//将e插入栈顶
	S -> top ++;				//修改栈顶指针
	return TRUE;
}

Status GetTop (SeqStack *S, ElemType *e)
{	//若栈不空，则用e返回栈顶元素
	if (S->top == 0)  return FALSE;
	*e = S->elem[S->top - 1];		//保存栈顶元素
	return TRUE;
}

Status Pop (SeqStack *S, ElemType *e)
{	//若栈不空，将栈顶元素弹出，并用e返回其值
	if (S -> top == 0)  
		return FALSE;
	else
	{
		S -> top --;			//修改栈顶指针
		*e = S -> elem[S -> top];	//保存栈顶元素
		return TRUE; 
	}
}

//全局变量 
SeqStack S;
char C[MAXSIZE];

int main()
{
	int i;
	ElemType e;
	scanf("%s",C);
	for(i=0;C[i]!='\0';i++)
	{
		if((C[i]>='A' && C[i]<='Z') || (C[i]>='a' && C[i]<='z'))
			printf("%c",C[i]);
		else if(C[i]=='+' || C[i]=='-')
		{
			while(GetTop(&S,&e)==TRUE)
			{
				if(e=='+' || e=='-' || e=='*' || e=='/')
				{
					Pop(&S,&e);
					printf("%c",e);
				}
				else
					break;
			}
			Push(&S,C[i]);
		}
		else if(C[i]=='*' || C[i]=='/')
		{
			while(GetTop(&S,&e)==TRUE)
			{
				if(e=='*' || e=='/')
				{
					Pop(&S,&e);
					printf("%c",e);
				}
				else
					break;
			}
			Push(&S,C[i]);
		}
		else if(C[i]=='(')
		{
			Push(&S,C[i]);
		}
		else
		{
			while(GetTop(&S,&e)==TRUE)
			{
				if(e=='(')
				{
					Pop(&S,&e);
					break;
				}
				else
				{
					Pop(&S,&e);
					printf("%c",e);
				}
			}
		}
	}	
	while(Pop(&S,&e)==TRUE)
	{
		printf("%c",e);
	}
	printf("\n");
	return 0;
}

C++ :

#include<iostream>
#include<cstring>
#include<stack>
#include<cstdio>
using namespace std;
string s;
stack<char> a;
bool isoperator(char);
int getpre(char,bool);
void work();
int main()
{
	//freopen("hz.in","r",stdin);
	//freopen("hz.out","w",stdout);
	cin>>s;	
	work();
	return 0;
}
void work()
{
	int i;
	for(i=0;i<s.size();++i)
	{
		if(!isoperator(s[i]))
		{
			cout<<s[i];
			continue;
		}
		else
		{
			if(a.empty())
			{
				a.push(s[i]);
				continue;
			}
			else
			{
				if(s[i]==')')
				{				
					while(a.top()!='('&& !a.empty())
					{
						cout<<a.top();
						a.pop();					
					}
					a.pop();
					continue;				
				}					
				while(!a.empty()&&getpre(s[i],false)<=getpre(a.top(),true))
				{
					cout<<a.top();
					a.pop();
				}
				a.push(s[i]);
			}						
		}		
	}
	while(!a.empty())
	{
		cout<<a.top();
		a.pop();
	}
}
bool isoperator(char ch)
{
	if(ch=='+'||ch=='-'||ch=='*'||ch=='/'||ch==')'||ch=='(')return true;
	else return false;
}
int getpre(char ch,bool flag)
{
	if(ch=='+'||ch=='-') return 1;
	if(ch=='*'||ch=='/') return 2;
	if(ch=='('&&flag) return 0;
	if(ch=='('&&!flag) return 3;
}

Pascal :

program acmb;
type
stack=array[1..200] of char;
var
top,i,j,h:integer;
ch,w:char;
a,s:stack;
st:string;
Function t(p1:char):integer;
begin
  case p1 of
      '#':t:=-1;
     '(':t:=0;
     '+':t:=1;
     '-':t:=1;
     '*':t:=2;
      '/':t:=2;
     ')':t:=3;
  end;
end;

procedure push(vars:stack;ch:char);
begin
inc(top);
s[top]:=ch;
end;

procedure pop(vars:stack);
begin
dec(top);
end;

function readtop(s:stack):char;
begin
readtop:=s[top];
end;
begin
  readln(st);
  st:=st+'#';
  push(s,'#');
  j:=1;
  i:=1;
  ch:=st[i];
  while ch<>'#'do
   begin
      if (ch in['A'..'Z']) or (ch in ['a'..'z']) then
       begin
         while (ch in['A'..'Z']) or (ch in ['a'..'z'])   do
            begin
              a[j]:=ch;
              inc(j);
              inc(i);
              ch:=st[i];
            end;
         {inc(j);}
   end
else
begin
   case ch of
      '+','-','*','/':  begin
                            w:=readtop(s); {取出栈顶符号}
                            while t(ch)<=t(w)do
                            begin
				   a[j]:=w;inc(j);
				   pop(s);
                              w:=readtop(s);
                            end;
				push(s,ch);
                         end;
'(':push(s,ch);
')':begin
		while s[top]<>'('do
                  begin
                    a[j]:=s[top];inc(j);
                     pop(s);
                  end;
		top:=top-1;
        end;
  end;   {end case}
inc(i);
ch:=st[i];
end;
end;
  w:=readtop(s);
while w<>'#' do
begin
	a[j]:=w;inc(j);
	pop(s);w:=readtop(s);
end;
a[j]:='#';pop(s);
h:=1;
repeat
	write(a[h]);inc(h);
until a[h]='#';
writeln;
end.