C :

#include<stdio.h>
#include<math.h>
#define maxn 101
int push1(int n,double *p,double v)
{
	n++;
	p[n]=v;
	return n;
}
double pop1(int n,double *p)
{
	return p[n];
}
int push2(int n,char *p,char v)
{
	n++;
	p[n]=v;
	return n;
}
int main()
{
	char str[maxn],stackope[maxn],op;
	int nn=0,np=0,i;
	double stacknum[maxn],sec,fir;
	scanf("%s",str);
	for(i=0;str[i]!='@';i++)
	{
		if(str[i]>='0'&&str[i]<='9')
		nn=push1(nn,stacknum,(str[i]-'0')*1.00);
		else
		{
		   if(np==0) np=push2(np,stackope,str[i]);
		  else if(str[i]=='(') np=push2(np,stackope,str[i]);
		  else if(str[i]==stackope[np]) 
		   {
		   	 sec=pop1(nn,stacknum);nn--;
		   	 fir=pop1(nn,stacknum);nn--;
		   	 if(str[i]=='+') { nn=push1(nn,stacknum,fir+sec);}
		   	 if(str[i]=='-') { nn=push1(nn,stacknum,fir-sec);}
		   	 if(str[i]=='*') { nn=push1(nn,stacknum,fir*sec);}
		   	 if(str[i]=='/') { nn=push1(nn,stacknum,fir/sec);}
		   	}
		   	else if(str[i]=='+')
		   	{
		   		if(stackope[np]=='*') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir*sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			    else if(stackope[np]=='/') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir/sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			     else if(stackope[np]=='-') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir-sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			    else
			      np=push2(np,stackope,str[i]);
		   		
		   	 }
		   	 else if(str[i]=='-')
		   	{
		   		if(stackope[np]=='*') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir*sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			    else if(stackope[np]=='/') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir/sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			     else if(stackope[np]=='+') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir+sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
		   		else
		   		  np=push2(np,stackope,str[i]);
		   	}
		   	else if(str[i]=='*'||str[i]=='/')
		   	{
		   		if(stackope[np]=='*') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir*sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			    else if(stackope[np]=='/') 
		   		{
		   		  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      nn=push1(nn,stacknum,fir/sec);np--;
		   	      np=push2(np,stackope,str[i]);
			    }
			    else
			      np=push2(np,stackope,str[i]); 
                		   		
		   	}
		   	else if(str[i]=='^')
		   	 {
		   	   sec=pop1(nn,stacknum);nn--;
		   	   nn=push1(nn,stacknum,pow(sec,(str[i+1]-'0')));
		   	   i=i+1;
		   	   continue;
		   	}
		   	else
		   	  {
		   	  	while(stackope[np]!='(')
		   	  	{
		   	  	  sec=pop1(nn,stacknum);nn--;
		   	      fir=pop1(nn,stacknum);nn--;
		   	      op=stackope[np];
		   	      if(op=='+') nn=push1(nn,stacknum,fir+sec);
		   	      if(op=='-') nn=push1(nn,stacknum,fir-sec);
		   	      if(op=='*') nn=push1(nn,stacknum,fir*sec);
		   	      if(op=='/') nn=push1(nn,stacknum,fir/sec);
		   	      np--;
		   	  	}
		   	  	np--;
		   	  }
		   }
		    
		}
		while(np!=0)
		{
		 sec=pop1(nn,stacknum);nn--;
	     fir=pop1(nn,stacknum);nn--;
		  op=stackope[np];
  	      if(op=='+') nn=push1(nn,stacknum,fir+sec);
	      if(op=='-') nn=push1(nn,stacknum,fir-sec);
		  if(op=='*') nn=push1(nn,stacknum,fir*sec);
		  if(op=='/') nn=push1(nn,stacknum,fir/sec);
		   	np--;
		}
		printf("%d",(int)stacknum[nn]);
		
	
	return 0;
}

C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<string>

using namespace std;

int a[101],i=0,p=1;
char sy[101],t[256];
string s;

void push()
{
	sy[++p]=s[i];
}

void pop()
{
	switch(sy[p--])
	{
		case '+':
			a[p]+=a[p+1];
			break;
		case '-':
			a[p]-=a[p+1];
			break;
		case '*':
			a[p]*=a[p+1];
			break;
		case '/':
			a[p]/=a[p+1];
			break;
	}
}
bool can()
{
	if((s[i]=='+'||s[i]=='-')&&sy[p]!='(') return 1;
	if((s[i]=='*'||s[i]=='/')&&(sy[p]=='*'||sy[p]=='/')) return 1;
	return 0;
}

int main()
{
	cin>>s;
	s[s.length()-1]=')';
	sy[p]='(';
	while(i<s.length())
	{
		while(s[i]=='(')
		{
			push();
			i++;
		}
		int x=0;
		while(s[i]>='0'&&s[i]<='9')
			x=x*10+s[i++]-'0';
		a[p]=x;
		do
		{
			if(s[i]==')')
			{
				while(sy[p]!='(')
					pop();
				a[--p]=a[p+1];
			}
			else
			{
				while(can())
					pop();
				push();
			}
			i++;
		}while(i<s.length()&&s[i-1]==')');
	}
	cout<<a[0];
	return 0;
}

Pascal :

const
  max=100;
var
  number:array[0..max] of longint;
  symbol:array[1..max] of char;
  s,t:string;
  i,p,j,code:integer;
procedure push;
begin
  inc(p);
  symbol[p]:=s[i];
end;
procedure pop;
begin
  dec(p);
  case symbol[p+1] of
   '+':inc(number[p],number[p+1]);
   '-':dec(number[p],number[p+1]);
   '*':number[p]:=number[p]*number[p+1];
   '/':number[p]:=number[p] div number[p+1];
  end;
end;
function can:boolean;
begin
  can:=true;
  if (s[i] in ['+','-']) and (symbol[p]<>'(')then exit;
  if (s[i] in ['*','/']) and (symbol[p] in ['*','/'])then exit;
   can:=false;
  end;
begin
    readln(s);
    s:=copy(s,1,length(s)-1);
    s:='('+s+')';
    i:=1;
    p:=0;
    while i<=length(s) do
      begin
        while s[i]='(' do
          begin
            push;
            inc(i);
          end;
    j:=i;
    repeat
      inc(i);
      until (s[i]<'0')or(s[i]>'9');
      t:=copy(s,j,i-j);
      val(t,number[p],code);
        repeat
          if s[i]=')' then
            begin
              while symbol[p]<> '(' do pop;
              dec(p);
              number[p]:=number[p+1];
            end
          else
          begin
            while can do
              pop;
              push;
            end;
          inc(i);
          until(i>length(s)) or (s[i-1]<>')');
        end;
      writeln(number[0]);
end.