如何使用VC库函数中的快速排序函数

int cmp(const void *x, const void *y)
{
 return *(int*)x - *(int*)y;
}
qsort(a, MAXN, sizeof(a[0]), cmp);

int cmpDouble(const void *x, const void *y)
{
 return (*(double*)x > *(double*)y ? 1 : -1);
}
qsort(a, n, sizeof(a[0]), cmpDouble);

struct Student
{
 char szName[30];
 int  nAge;
};

int cmpStudent (const void *x, const void *y)
{   //先作下指针转换，再按要求比较
 Student *pnodex = (Student*)x, *pNodey = (Student*)y;
 if (pNodex->nAge != pNodey->nAge)
  return pNodex->nAge - pNodey->nAge;
 else
  return strcmp(pNodex->szName, pNodey->szName);
}
qsort(a, n, sizeof(a[0]), cmpStudent);

int cmp1(const void *x, const void *y)
{
 char *pcx = (char*)x, *pcy = (char*)y;

 bool flag1 = *pcx >= 'A' && *pcx <= 'Z';
 bool flag2 = *pcy >= 'A' && *pcy <= 'Z';

 if(flag1 == flag2)    //如果都为大写字母或都为小写字母
  return *pcx - *pcy;
 else                  //否则，谁为大写字母，谁的权值小。
  return flag1 ? -1 : 1;
}
int main()
{
 char szText[] = "AajkuKdYUBCDwyz";
 qsort(szText, strlen(szText), sizeof(szText[0]), cmp1);
 printf("%s\n", szText);
 return 0;
}