数据结构表达式解析使用Stack

#include<stdio.h>
#include<string.h>

//char stack
char stack[25];
int top = -1;

void push(char item) {
   stack[++top] = item;
}

char pop() {
   return stack[top--];
}

//returns precedence of operators
int precedence(char symbol) {

   switch(symbol) {
      case '+':
      case '-':
         return 2;
         break;
      case '*':
      case '/':
         return 3;
         break;
      case '^':
         return 4;
         break;
      case '(':
      case ')':
      case '#':
         return 1;
         break;
   }
}

//check whether the symbol is operator?
int isOperator(char symbol) {

   switch(symbol) {
      case '+':
      case '-':
      case '*':
      case '/':
      case '^':
      case '(':
      case ')':
         return 1;
      break;
         default:
         return 0;
   }
}

//converts infix expression to postfix
void convert(char infix[],char postfix[]) {
   int i,symbol,j = 0;
   stack[++top] = '#';

   for(i = 0;i<strlen(infix);i++) {
      symbol = infix[i];

      if(isOperator(symbol) == 0) {
         postfix[j] = symbol;
         j++;
      } else {
         if(symbol == '(') {
            push(symbol);
         } else {
            if(symbol == ')') {

               while(stack[top] != '(') {
                  postfix[j] = pop();
                  j++;
               }

               pop();   //pop out (.
            } else {
               if(precedence(symbol)>precedence(stack[top])) {
                  push(symbol);
               } else {

                  while(precedence(symbol)<=precedence(stack[top])) {
                     postfix[j] = pop();
                     j++;
                  }

                  push(symbol);
               }
            }
         }
      }
   }

   while(stack[top] != '#') {
      postfix[j] = pop();
      j++;
   }

   postfix[j]='\0'; //null terminate string.
}

//int stack
int stack_int[25];
int top_int = -1;

void push_int(int item) {
   stack_int[++top_int] = item;
}

char pop_int() {
   return stack_int[top_int--];
}

//evaluates postfix expression
int evaluate(char *postfix){

   char ch;
   int i = 0,operand1,operand2;

   while( (ch = postfix[i++]) != '\0') {

      if(isdigit(ch)) {
         push_int(ch-'0'); // Push the operand
      } else {
         //Operator,pop two  operands
         operand2 = pop_int();
         operand1 = pop_int();

         switch(ch) {
            case '+':
               push_int(operand1+operand2);
               break;
            case '-':
               push_int(operand1-operand2);
               break;
            case '*':
               push_int(operand1*operand2);
               break;
            case '/':
               push_int(operand1/operand2);
               break;
         }
      }
   }

   return stack_int[top_int];
}

void main() {
   char infix[25] = "1*(2+3)",postfix[25];
   convert(infix,postfix);

   printf("Infix expression is: %s\n" , infix);
   printf("Postfix expression is: %s\n" , postfix);
   printf("Evaluated expression is: %d\n" , evaluate(postfix));
}