buffer problems in c

Ken H

13y1.5k

Hello everyone,

I met a buffer problem, my code is as follows (bold font):

#include

struct Student

{

int stu_id;

char stu_name[10];

int stu_age;

char stu_professional[10];

};

void rand_output(Student s)

{

printf("\t ID\tname\tage\tpro\n");

printf("\t%d\t%s\t%d\t%s\n",s.stu_id,s.stu_name,s.stu_age,s.stu_professional);

}

int main()

{

char answer='Y';

int get_randNumber;

Student stu[3]={{201301,"Ken",18,"computer"},{201302,"Mary",17,"computer"},

{201303,"Jack",18,"computer"}};

while (toupper(answer)=='Y')

{

// fflush(stdin); // Assuming it is commented

srand((unsigned)time(NULL));

get_randNumber=rand()%(2-0+1)+0;

rand_output(stu[get_randNumber]);

/*fflush(stdin);If the line is commented out,

The following code will not be executed in the second to(while loop will be aborted). Why is there such a situation?

Now, I would like to know its compiler theory.*/

printf("\tYou like to continue anyway?(Y or N):");

scanf("%c",&answer);

system("cls");

}

return 0;

}

Regards,

Ken

4 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes13y ago
Accepted answer
When you press 'y' on the first iteration of the while loop you also have to press the return key.

Now, scanf only consumes the 'y' - it doesn't consume the '\n' which is still in the input buffer.

On the next iteration of the while loop, if the buffer hasn't been flushed, scanf just reads the '\n' - it ignores the second 'y' and '\n' that have just been input. As 'answer' now contains '\n' rather than 'y', the while loop (and the program) ends prematurely.
Ken H13y ago
Thank you for your explanation. :)
Vulpes13y ago
Yes, that's right Ken.

On the second iteration scanf reads the '\n' left behind from the first iteration.

When calling scanf multiple times, you have to remember to clear the buffer each time to avoid this sort of problem.
Ken H13y ago
Well, this while loop, the second iteration is encountered again 'scanf function, it will read the first time I press the Enter key (the' \ n ') as 'answer 'values.Is like this do?

thank for you.