判断表达式括号是否匹配，C语言堆栈实现

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#define STACK_INIT_SIZE 100

#define STACKINCREMENT  10

typedef struct Sq{
char *base;
char *top;
int stacksize;

}SqStack;

void InitStack(SqStack *s)

{
s->base =(char *)malloc(STACK_INIT_SIZE*sizeof(char));
if(!s->base )
exit(0);
s->top =s->base ;
s->stacksize =STACK_INIT_SIZE;

}

void Push(SqStack *s,char e)

{
if(s->top -s->base ==s->stacksize )
s->base =(char *)realloc(s->base ,(s->stacksize +STACKINCREMENT)*sizeof(char));
if(!s->base )
exit(0);
s->stacksize +=STACKINCREMENT;
*(s->top )=e;
s->top ++;

}

void GetTop(SqStack *s,char *e)

{
if(s->top ==s->base )
exit(0);
*e=*(s->top -1);

}

void Pop(SqStack *s)

{
if(s->top ==s->base )
exit(0);
s->top --;

}

int main()

{
SqStack *s;
s=(SqStack *)malloc(sizeof(SqStack));
InitStack(s);
int flag=1;
int i=0;
char str[128];
gets(str);
char *e=(char *)malloc(sizeof(char));
while(str[i]!='\0'&&flag)
{
switch(str[i])
{
case '[':Push(s,str[i]);break;
case '{':Push(s,str[i]);break;
case '(':Push(s,str[i]);break;
case ']':if(s->top !=s->base )
{
GetTop(s,e);
if(*e=='[')
{
Pop(s);
flag=1;
break;
}
else flag=0; break;
}
else flag=0;break;
case ')':if(s->top !=s->base )
{
GetTop(s,e);
if(*e=='(')
{
Pop(s);
flag=1;
break;
}
else flag=0; break;
}
else flag=0;break;
case '}':if(s->top !=s->base )
{
GetTop(s,e);
if(*e=='{')
{
Pop(s);
flag=1;
break;
}
else flag=0; break;
}
else flag=0;break;
default:break;
}
i++;
}
if(s->base ==s->top )
flag=0;
if(flag==1)
printf("YES!\n");
else printf("NO!\n");
return 0;

}