数据结构括号匹配问题

#include<stdio.h>
#include<malloc.h>
#include<string.h>
#define STACK_INIT_SIZE 10
#define STACKINCREMENT 5

#define OK 1
#define ERROR 0
typedef char ElemType;
typedef struct { /*建立一个栈的首结点*/
    ElemType * base;
    ElemType * top;
    int stacksize;
} SqStack;
int InitStack(SqStack *s) { /*建立空的栈并返回首地址*/
    s->base=((ElemType*)malloc(STACK_INIT_SIZE*sizeof(ElemType)));
    if (!s->base) return ERROR;
    s->top=s->base;
    s->stacksize=STACK_INIT_SIZE;
    return OK;
}
int StackEmpty(SqStack *s) { /*判断栈是否为空*/
    if (s->top==s->base) return OK;
    else                 return ERROR;
}
int Push(SqStack *s,ElemType e) { /*往栈顶插入元素即进栈*/
    if (s->top-s->base>=s->stacksize) { /*判断是否栈满*/
        s->base=((ElemType*)realloc(s->base,(s->stacksize+STACKINCREMENT)*sizeof(ElemType)));
        if (!s->base) return ERROR;
        s->stacksize+=STACKINCREMENT;
        s->top=s->base+s->stacksize;
    }
    *s->top++=e;
    return OK;
}
int Pop(SqStack *s,ElemType *e) { /*让栈顶元素依次输出即出栈*/
    if (StackEmpty(s)) return ERROR;
    *e=*(--s->top);
    return OK;
}
int Comp(ElemType a,ElemType b) {
    if ((a=='('&&b!=')')
      ||(a=='['&&b!=']')
        ||(a=='{'&&b!='}')) {
        return ERROR;
    } else return OK;
}
int Count(SqStack *s) {                                    //这一小段是什么意思啊 为什么STACK_INIT_SIZE得*2啊，后面又定义e1是干嘛？
    ElemType e[STACK_INIT_SIZE*2];
    ElemType e1;
    int i;

 
    InitStack(s);
    fgets(e,STACK_INIT_SIZE*2,stdin);                     fgets这个函数有什么用？这一段也看不懂
    if ('\n'==e[strlen(e)-1])
        e[strlen(e)-1]=0;
    printf("%s\n",e);
    for (i=0;e[i]!='\0';i++) {
        switch (e[i]) {
        case '(':
        case '[':
        case '{':
            Push(s,e[i]);
            break;
        case ')':
        case ']':
        case '}':
            if (StackEmpty(s)) {
                printf("%*s↖右括号多余\n",i+1,"");
                return(ERROR);
            } else Pop(s,&e1);
            if (!Comp(e1,e[i])) {
                printf("%*s↖左右匹配出错\n",i+1,"");
                return(ERROR);
            }
        }
    }
    if (!StackEmpty(s)) {
        printf("%*s↖左括号多余\n",i,"");
        return(ERROR);
    } else {
        printf("匹配正确\n");
        return(OK);
    }
}
void main() {
    SqStack s;
    Count(&s);
    free(s.base);
}