C Struct char members getting a weird values

Question

I just started to play C and I bump into this problem. Here's my code:

#include<stdio.h>
#include<conio.h>

struct person {
    int i;
    char name[100];
};

int main() {
    struct person p[2];

    clrscr();
    for(int i=0;i<2;i++) {
        printf("Enter i:\n");
        scanf("%d",&p[i].i);

        printf("Enter name:\n");
        gets(p[i].name);
    }
    for(int j=0;j<2;j++) {
        printf("ID: %d, Name: %c\n", p[j].i,p[j].name);
    }
    getch();
    return 0;
}

Here's a sample ouput:

enter image description here

The problem is, all char members are not being asked for a value.

UPDATE:

btw, I am using Turbo C++ version 3 compiler.

You probably need to clear the input buffer after typing in a number (you press enter after the number, but you don't read that enter) — Fox32, Jan 04 '12 at 17:38
Your question is Windows specific. Posix, Linux, MacOS don't have `` — Basile Starynkevitch, Jan 04 '12 at 17:40
You should enable all warnings in your compiler. With GCC, this is done with the `-Wall` flag. — Basile Starynkevitch, Jan 04 '12 at 17:41
user Mystical got it right, but then when i refreshed the page, it was deleted. — Loreto Gabawa Jr., Jan 04 '12 at 17:47
@jun Actually, no I didn't. `fflush(stdin);` is not allowed. I have fixed my answer. — Mysticial, Jan 04 '12 at 17:54

score 4 · Answer 1 · answered Jan 04 '12 at 17:37

4

You should print a string with %s; %c will interpret the pointer as a char. (Strictly, I believe the result is undefined behavior.)

answered Jan 04 '12 at 17:37

Fred Foo

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Yeah I just did that, but it's still the same. it never asked for the member 'name'. – Loreto Gabawa Jr. Jan 04 '12 at 17:41
From your program's output, it seems it did. – Fred Foo Jan 04 '12 at 17:44
Yes you are right about it. but the main issue was whenever a char members is asked for an input, it just jump to another loop. – Loreto Gabawa Jr. Jan 04 '12 at 17:53

Mysticial · Accepted Answer · 2012-01-04T17:50:25.740

3

Two things:

You need to clear the input buffer to keep it from eating the newline.
Secondly, you need to change the format string to %s.

Here's the corrected code:

int main() {
    struct person p[2];

    for(int i=0;i<2;i++) {
        printf("Enter i:\n");

        scanf("%d",&p[i].i);

        //  Flush input buffer
        int ch;
        while ((ch = getchar()) != '\n' && ch != EOF);


        printf("Enter name:\n");
        gets(p[i].name);
    }
    for(int j=0;j<2;j++) {
        printf("ID: %d, Name: %s\n", p[j].i,p[j].name);
    }
    getch();
    return 0;
}

%c expects a char, but you're trying to pass in a string. It's undefined behavior to have mismatching types.

Output:

Enter i:
1
Enter name:
asdf
Enter i:
2
Enter name:
zxcv
ID: 1, Name: asdf
ID: 2, Name: zxcv

edited Jan 04 '12 at 17:50

answered Jan 04 '12 at 17:40

Mysticial

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1

`fflush(stdin)` is undefined behaviour. `fflush` is defined only for output stream. [:)](http://stackoverflow.com/questions/2979209/using-fflushstdin) – another.anon.coward Jan 04 '12 at 17:43
Hi Mystical, for some strange reason when I accept your answer, a message pop-up and told me your answer was deleted. so what I did, I updated my question with your answer in it. thanks – Loreto Gabawa Jr. Jan 04 '12 at 17:54
@another.anon.coward pointed out the mistake I made. So I deleted to give me time to fix my answer. Although `fflush(stdin)` seems to work in MSVC, apparently it's undefined behavior by the standard. – Mysticial Jan 04 '12 at 17:58
I see. I really appreciated your help. – Loreto Gabawa Jr. Jan 04 '12 at 18:09

score 1 · Answer 3 · answered Jan 04 '12 at 17:43

You probably need to clear the input buffer after typing in a number (you press return after the number, but you don't read that return)

You can read the input stream until you read a \n after calling scanf:

while( ch = getchar() != '\n' && ch != EOF);

score 0 · Answer 4 · answered Jan 04 '12 at 17:39

Use sscanf as scanf is deprecated. You can also use sscanf for reading in strings as well, not just numbers. Also, %c is for printing characters.

#include<stdio.h>
#include<conio.h>

struct person {
    int i;
    char name[100];
};

int main() {
    struct person p[2];

    clrscr();
    for(int i=0;i<2;i++) {
        printf("Enter i:\n");
        sscanf("%d", &p[i].i);

        printf("Enter name:\n");
        sscanf("%s", p[i].name);
    }
    for(int j=0;j<2;j++) {
        printf("ID: %d, Name: %s\n", p[j].i,p[j].name);
    }
    getch();
    return 0;
}

You should either be very sure about what you write or use a compiler. — duedl0r, Jan 04 '12 at 17:45

score 0 · Answer 5 · answered Jan 04 '12 at 17:41

0

You should either use %s instead. Expression p[j].name is a pointer to an array of chars, so you can't print it with %c.

answered Jan 04 '12 at 17:41

Phonon

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C Struct char members getting a weird values

5 Answers5