C语言小函数

#include <stdio.h>#include <stdlib.h>#include <assert.h>typedef struct Intstack{    int *elems;    int loglength;    int alloclength;} Intstack;void IntstackNew(Intstack *s){    s->loglength=0;    s->alloclength=4;    s->elems=malloc(4*sizeof(int));    assert(s->elems!=NULL);}void IntstackFree(Intstack *s){    free(s->elems);}void IntstackPush(Intstack *s, int value){    if(s->alloclength==s->loglength)    {        s->alloclength *= 2;        s->elems=realloc(s->elems, s->alloclength*sizeof(int));        assert(s->elems!=NULL);    }    s->elems[s->loglength] = value;    s->loglength++;}int IntstackPop(Intstack *s){    assert(s->loglength>0);    s->loglength--;    return s->elems[s->loglength];}int main(){    Intstack s;    IntstackNew(&s);    IntstackPush(&s, 4);    IntstackPush(&s, 5);    printf("%d\n", IntstackPop(&s));    printf("%d\n", IntstackPop(&s));    IntstackFree(&s);    printf("Hello world!\n");    return 0;}