用栈来实现 括号匹配

#include<stdio.h>
#include<stdlib.h>
#define STACK_INIT_SIZE 100
#define STACKINCREMENT 10
#define OK 1
#define ERROR 0
#define OVERFLOW -2
typedef int Status;
typedef char SElemType;
typedef struct
{
    SElemType *base;
    SElemType *top;
    int stacksize;
} SqStack;
Status InitStack(SqStack *S)
{
    S->base=(SElemType *)malloc(STACK_INIT_SIZE*sizeof(SElemType));
    S->top=S->base;
    S->stacksize=STACK_INIT_SIZE;
    return OK;
}
Status StackEmpty(SqStack *S)
{
    if(S->top!=S->base) return ERROR;
    return OK;
}
Status Push(SqStack *S,SElemType e)
{
    if(S->top-S->base>=S->stacksize)
    {
        S->base=(SElemType*)realloc(S->base,(S->stacksize+STACKINCREMENT)*sizeof(SElemType));
        if (!S->base)exit(OVERFLOW);
        S->top=S->base+S->stacksize;
        S->stacksize+=STACKINCREMENT;
    }
    *S->top++=e;
    return OK;
}
Status Pop(SqStack *S,SElemType*e)
{
    if(S->top==S->base) return ERROR;
    *e=*--S->top;
    return OK;
}
Status Bracket(SqStack *S,char *str)
{
    int i=0,flag1=0,flag2;
    SElemType e;
    while(str[i]!='\0')
    {
        switch(str[i])
        {
        case '(':
            Push(S,'(');
            break;
        case '[':
            Push(S,'[');
            break;
        case '{':
            Push(S,'{');
            break;
        case ')':
        {
            if(StackEmpty(S))
            {
                flag1=1;
                break;
            }
            Pop(S,&e);
            if(e!='(')
                flag1=1;
            break;
        }
        case ']':
        {
            if(StackEmpty(S))
            {
                flag1=1;
                break;
            }
            Pop(S,&e);
            if(e!='[')
                flag1=1;
            break;
        }
        case '}':
        {
            if(StackEmpty(S))
            {
                flag1=1;
                break;
            }
            Pop(S,&e);
            if(e!='{')
                flag1=1;
            break;
        }
        default:
            break;
        }
        if(flag1) break;
        i++;
    }
    flag2=StackEmpty(S);
    if(!flag1 && flag2) printf("It is ok!\n");
    else printf("It is error!\n");
    return OK;
}
int  main()
{
    char str[255];
    SqStack S;
    InitStack(&S);
    printf("enter a cross:");
    scanf("%s",str);
    Bracket(&S,str);
    printf("\n");
}