程序代码：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define STACK_INIT_SEZE 100
#define STACKINCREMENT 10
#define OVERFLOW -1
#define OK 0;
#define ERROR -2;
typedef int SElemType;
typedef struct {
    SElemType *base;
    SElemType *top;
    int stacksize;
}SqStack;
int Initstack(SqStack *s){
    s->base=(SElemType*)malloc(STACK_INIT_SEZE*sizeof(SElemType));
    if(!s->base) return OVERFLOW;
    s->top=s->base;
    s->stacksize=STACK_INIT_SEZE;
    return OK;
}//initstack
int Push (SqStack *s,SElemType e){
    if(s->top-s->base>=s->stacksize){
        s->base=(SElemType*)realloc(s->base,(s->stacksize+STACK_INIT_SEZE)*sizeof(SElemType));
        if(!s->base) return OVERFLOW;
        s->top=s->base+s->stacksize;
        s->stacksize+=STACKINCREMENT;
    }
    *s->top=e;
    return OK;
}//push
int Pop(SqStack *s,SElemType e){
    if(s->top==s->base) return ERROR;
    e=*--s->top;
    return OK;
}//POP
int DestroyStack(SqStack *s){
    SElemType *p;
    for(p=s->top;s->top!=s->base;p=s->top){
        --s->top;
        free(p);
    }
    if(s->top==s->base)
        return 0;
}
int main(){
    int i=0;
    char x,a[STACK_INIT_SEZE];
    SqStack *s;
    Initstack(s);
    printf("Please input the srings:\n");
    gets a;
    while(a[i]!=&){
        Push(s,a[i]);
        i++;
    }
    if(!a[i]) printf("The elements before and after @ do not equal! ");
    i++;
    while(a[i]){
        Pop(s,x);
        if(x!=a[i]){
            DestroyStack(s);
            printf("The elements before and after @ do not equal! ");
        }
        i++;
    }
        printf("The elements before and after @ equal! ");
}