Stop 함수를 실행하면 가장 마지막에 들어간 데이터가 보여져야하는데 나오질 않네요ㅠㅠ 고수님들 무엇인 문제인지 아시나요?

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define TRUE 1
#define FALSE 0  
#define STACK_LEN 10001


typedef struct _Stack
{
    int arr[STACK_LEN];
    int topIndex;
}  ST;

void SstackInit(ST *pstack)
{
    pstack->topIndex = -1;
}

void Spush(ST *pstack, int X)
{
    pstack->topIndex += 1;
    pstack->arr[pstack->topIndex] = X;
}

int Sempty(ST *pstack)
{
    if (pstack->topIndex == -1)
        return TRUE;
    else
        return FALSE;
}

int Spop(ST *pstack)
{
    int imsi;

    if (Sempty(pstack))
    {
        printf("error!");
        return -1;
    }

    imsi = pstack->topIndex;
    pstack->topIndex -= 1;
    return pstack->arr[imsi];

}   

int Ssize(ST *pstack)
{   
    return pstack->topIndex + 1;     //-1부터 시작이니깐

}

int Stop(ST *pstack)
{
    if (Sempty(pstack))
    {
        return -1;
    }

    return pstack->arr[pstack->topIndex];
}


int   main()
{
    ST stack;
    char str[10];
    int N = 0, i, num;


    scanf("%d", &N);

    SstackInit(&stack);

    for (i = 0; i < N; i++)
    {
        scanf("%s", str);


        if (!strcmp(str, "push"))
        {
            scanf("%d", &num);

            Spush(&stack, num);
        }

        else if (!strcmp(str, "pop"))
        {
            printf("%d\n", Spop(&stack));
        }


        else if (!strcmp(str, "size"))
        {
            printf("%d\n", Ssize(&stack));
        }


        else if (!strcmp(str, "empty"))
        {
            printf("%d\n",Sempty(&stack));
        }

        else if (!strcmp(str, "top"))
        {
            printf("%d\n", Stop(&stack));
        }



    }

    return 0;
}

Stop 함수를 실행하면 가장 마지막에 들어간 데이터가 보여져야하는데 나오질 않네요ㅠㅠ 고수님들 무엇인 문제인지 아시나요?

include

include

include

define TRUE 1

define FALSE 0

define STACK_LEN 10001

typedef struct _Stack { int arr[STACK_LEN]; int topIndex; } ST;

void SstackInit(ST *pstack) { pstack->topIndex = -1; }

void Spush(ST *pstack, int X) { pstack->topIndex += 1; pstack->arr[pstack->topIndex] = X; }

int Sempty(ST *pstack) { if (pstack->topIndex == -1) return TRUE; else return FALSE; }

int Spop(ST *pstack) { int imsi;

if (Sempty(pstack))
{
    printf("error!");
    return -1;
}

imsi = pstack->topIndex;
pstack->topIndex -= 1;
return pstack->arr[imsi];

}

int Ssize(ST *pstack) {
return pstack->topIndex + 1; //-1부터 시작이니깐

}

int Stop(ST *pstack) { if (Sempty(pstack)) { return -1; }

return pstack->arr[pstack->topIndex];

}

int main() { ST stack; char str[10]; int N = 0, i, num;

scanf("%d", &N);

SstackInit(&stack);

for (i = 0; i < N; i++)
{
    scanf("%s", str);


    if (!strcmp(str, "push"))
    {
        scanf("%d", &num);

        Spush(&stack, num);
    }

    else if (!strcmp(str, "pop"))
    {
        printf("%d\n", Spop(&stack));
    }


    else if (!strcmp(str, "size"))
    {
        printf("%d\n", Ssize(&stack));
    }


    else if (!strcmp(str, "empty"))
    {
        printf("%d\n",Sempty(&stack));
    }

    else if (!strcmp(str, "top"))
    {
        printf("%d\n", Stop(&stack));
    }



}

return 0;

}