warning C4013: 'malloc' undefined; assuming extern returning int

#include<stdio.h>
main()
{
    struct stu
    {
        int num;
        char*name;
        char sex;
        float score;
    }*ps;
    ps=(struct stu*)malloc(sizeof(struct stu));
    ps->num=102;
    ps->name="Zhang ping";
    ps->sex='M';
    ps->score=62.5;
    printf("Number=%d\nName=%s\n",ps->num,ps->name);
    printf("Sexr=%c\nScore=%f\n",ps->sex,ps->score);
    free(ps);
}