C语言实现逆波兰表达式

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define STACK_INIT_SIZE 20
#define STACKINCREMENT 10
#define MAXBUFFER 10

typedef double ElemType;

typedef struct
{
ElemType *base;
ElemType *top;
int stackSize;
}sqStack;

/*
**栈的初始化
*/

void InitStack(sqStack *s)
{
s->base=(ElemType *)malloc(STACK_INIT_SIZE*sizeof(ElemType));
if(!s->base)
exit(0);
s->top=s->base;
s->stackSize=STACK_INIT_SIZE;
}

/*
**入栈操作
*/
void Push(sqStack *s,ElemType e)
{
if(s->top-s->base==s->stackSize)
{
s->base=(ElemType *)realloc(s->base,(STACKINCREMENT+s->stackSize)*sizeof(ElemType));
if(!s->base)
exit(0);

s->top=s->base+s->stackSize;
s->stackSize=s->stackSize+STACKINCREMENT;
}
*(s->top)=e;
s->top++;
}

/*
**出栈操作
*/
void Pop(sqStack *s,ElemType *e)
{
if(s->top==s->base)
return;
*e=*--(s->top);
}

/*
**计算栈的容量
*/
int StackLen(sqStack *s)
{
return (s->top-s->base);
}
/*
**逆波兰表达式
**正常表达式--->逆波兰表达式
**a+b--->a b +
**a+(b-c)--->a b c - +
**a+(b-c)*d--->a b c - d * +
**a+d*(b-c)--->a d b c - * +
*/
int main()
{
sqStack s;
char c;
double d,e;
char str[MAXBUFFER];
int i=0;

InitStack(&s);
printf("请输入逆波兰表达式输入待计算数据，数据与运算符之间用空格隔开，以#作为结束标志：\n");

scanf("%c",&c);
while(c!='#')
{
while(isdigit(c)||c=='.')
{
str[i++]=c;
str[i]='\0';
if(i>=10)
{
printf("error");
return -1;
}

scanf("%c",&c);
if(c==' ')
{
d=atof(str);
Push(&s,d);
i=0;
break;
}
}
switch(c)
{
case '+':
Pop(&s,&e);
Pop(&s,&d);
Push(&s,d+e);
break;
case '-':
Pop(&s,&e);
Pop(&s,&d);
Push(&s,d-e);
break;
case '*':
Pop(&s,&e);
Pop(&s,&d);
Push(&s,d*e);
break;
case '/':
Pop(&s,&e);
Pop(&s,&d);
if(e!=0){
Push(&s,d/e);
}
else
{
printf("error!");
return -1;
}
break;
}
scanf("%c",&c);
}
Pop(&s,&d);
printf("the final result:%f",d);
return 0;
}