萌新求问，关于C语言函数返回值的问题

Question

有没有大佬解释一下为什么第一段程序改成第二段程序运行就出错啊，跪谢。
一：
#include
#include
#include

typedef struct student{
char size[6];
float score;
struct student* next;
} Student;

int main()
{
int n=1;
char input[7];
Student *head=NULL;
Student *current, *end;
printf("please input the size of the student No.%d\n",n);
while(gets(input)!=NULL && input[0]!='0')
{
current=(Student *)malloc(sizeof(Student));
if(head==NULL)
{
head=current;
} else {
end->next=current;
}
printf("please input the score of the student No.%d\n",n);
strcpy(current->size,input);
scanf("%f",&current->score);
while(getchar()!='\n')
{
continue;
}
current->next=NULL;
n++;
printf("please input the size of the student No.%d\n",n);
end=current;
}

Student *headl=NULL;
headl=head;
if(headl==NULL)
{
    printf("No list entered!!!!!!!!\n");
}
while( headl!=NULL )
{
    printf("the student with a school number of %6s have a score of %4.2f\n",headl->size,headl->score);
    headl=headl->next;
}

while( headl!=NULL )
{
    free(headl);
    headl->next=headl;
} 
return 0;   

}

二：
#include
#include
#include

typedef struct student{
char size[6];
float score;
struct student* next;
} Student;

Student *add( Student *head );
void printfl( Student *head );
void freel( Student *head );

int main()
{
Student *head=NULL, *headl=NULL;
head=add(head);
printfl(head);
free(head);
return 0;
}

Student *add( Student *head )
{
int n=1;
char input[7];
Student *headl=NULL;
headl=head;
Student *current, *end;
printf("please input the size of the student No.%d\n",n);
while(gets(input)!=NULL && input[0]!='0')
{
if(headl==NULL)
{
headl=current;
} else {
end->next=current;
}
current=(Student *)malloc(sizeof(Student));
printf("please input the score of the student No.%d\n",n);
strcpy(current->size,input);
current->next=NULL;
scanf("%f",&current->score);
while(getchar()!='\n')
{
continue;
}
n++;
printf("please input the size of the student No.%d\n",n);
end=current;
}
return headl;
}

void printfl( Student *head )
{
Student *headl=NULL;
headl=head;
if(headl==NULL)
{
printf("No list entered!!!!!!!!\n");
}
while( headl!=NULL )
{
printf("the student with a school number of %6s have a score of %f\n",headl->size,headl->score);
headl=headl->next;
}
}

void freel( Student *head )
{
Student *headl=NULL;
headl=head;
while( headl!=NULL )
{
free(headl);
headl->next=headl;
}
}

Answer 1

可以单步debug啊，这样你就知道出错的信息和出错的位置了。