#include <stdlib.h>
struct stack {
   int data;
   struct stack *next;
};
typedef struct stack s_list;
typedef s_list *link;

link operator = NULL;
link operand  = NULL;
void push(char ff,int value) {
   link node;
   node = ( link ) malloc(sizeof(s_list));
   node->data = value;
   if (ff == 1) { node->next = operator; operator = node; }
   else { node->next=operand; operand=node; }
}

int pop(char ff) {
   link top;  int value;
   if (ff == 1) {
     if (operator != NULL )  {
       top = operator;
       operator = operator->next;
       value = top->data;
       free(top);
     }
     else  value = -1;
   }
   else {
     if (operand != NULL )  {
       top = operand;
       operand = operand->next;
       value = top->data;
       free(top);
     }
     else  value = -1;
   }
   return value;
}

int empty(link stack) {
   if ( stack == NULL ) return 1;  else  return 0;
}

int isoperator(char op) {
   switch (op) {
      case '(':
      case ')':
      case '+':
      case '-':
      case '*':
      case '^':
      case '/': return 1;
      default:  return 0;
   }
}

int prior(int op)
{
   switch ( op ) {
      case '^': return 3;
      case '*':
      case '/': return 2;
      case '+':
      case '-': return 1;
      default:  return 0;
   }
}

int get_value(int op,int operand1,int operand2)
{
   switch ( (char) op )
   {
      case '*': return ( operand1 * operand2 );
      case '/': return ( operand1 / operand2 );
      case '+': return ( operand1 + operand2 );
      case '-': return ( operand1 - operand2 );
   }
}
void main()
{
   char exp[100];
   int op = 0, s1=0, operand1 = 0, operand2 = 0, result = 0, pos = 0,k;

   printf("input expression ==> "); gets(exp);
   while ( exp[pos] != '\0' && exp[pos] != '\n' ) {
    if (isoperator(exp[pos])) { /* '+ - * /' */
     if (exp[pos] == '(') push(1,'(');
      else
	if (exp[pos] == ')') {
          push(2,s1); s1=0;
          while (!empty(operator) && (op=pop(1))!='(') {
            operand2=pop(2); operand1=pop(2);
            push(2, (k=get_value(op,operand1,operand2)));
	    printf("%d%c%d=%d\n",operand1,op,operand2,k);
	  }
	}
        else {
	 if (s1 != 0) { push(2, s1); s1=0; }
         if ( !empty(operator) )
           while (prior(exp[pos]) <= prior(operator->data) &&
                   !empty(operator)) {
             op=pop(1); operand2=pop(2); operand1=pop(2);
             push(2, (k=get_value(op,operand1,operand2)));
             printf("%d%c%d=%d\n",operand1,op,operand2,k);
           }
         push(1,exp[pos]);
        }
    }
    else s1=s1*10+exp[pos]-48;
    pos++;
   }
   if (s1 != 0) push(2,s1);
   while ( !empty(operator) ) {
     op = pop(1); operand2 = pop(2); operand1 = pop(2);
     push(2,(k=get_value(op,operand1,operand2)));
   }
   result = pop(2); printf("%s=%d\n",exp,result);
}