infixtopostfix.c

实现中缀表达式向后缀表达式的转换。要求： 键盘输入一个表达式

#include <stdio.h>

#define MAX_EXPR_SIZE 100
#define MAX_STACK_SIZE 100
typedef enum {LPAREN,RPAREN,PLUS,MINUS,DIVIDE,TIMES,MOD,EOS,OPERAND} precedence;

static char expr[MAX_EXPR_SIZE];
static int stack[MAX_STACK_SIZE];
static int top=0;

static int isp[]={0,19,12,12,13,13,13,0};
static int icp[]={20,19,12,12,13,13,13,0};

void add(int* n, precedence token)
{
  stack[*n++]=token;
}

precedence delete(int* n)
{
  return stack[*n--];
}

precedence getToken(char* symbol, int* n)
{
  *symbol=expr[(*n)++];
  switch(*symbol){
    case '(' : return LPAREN;
    case ')' : return RPAREN;
    case '+' : return PLUS;
    case '-' : return MINUS;
    case '/' : return DIVIDE;
    case '*' : return TIMES;
    case '%' : return MOD;
    case ' ' : return EOS;
    default  : return OPERAND;
  }
}

void printToken(precedence token)
{
  printf("%d\t",token); 
}

void inToPost(void)
{
  char symbol;
  precedence token;
  int n=0;
  stack[0]=EOS;
  for(token=getToken(&symbol,&n); 
      token!=EOS;
      token=getToken(&symbol,&n)){
    if(token==OPERAND)
      printf("%c", symbol);
    else if(token==RPAREN){
      while(stack[top]!=LPAREN)
        printToken(delete(&top));
      delete(&top);
    }
    else{
      while(isp[stack[top]] >= icp[token])
        printToken(delete(&top));
      add(&top, token);
    }
  }
  while( (token=delete(&top)) != EOS)
    printToken(token);
   printf("\n");
}

int
main(int argc, char* argv[])
{
  return 0;
}