Some Newb Problem with "int", please help.

[Apotheosis]

The problem professor gave us is:

Write a program which reads two integer values. If the first is less
than the second, print the message "up". If the second is less than
the first, print the message "down" If the numbers are equal, print
the message "equal" If there is an error reading the data, print a
message containing the word "Error" and perform exit( 0 );
And this is what I wrote:

main()
{
int x;
int y;

printf("Enter the first integer: ");
scanf("%d", &x);

printf("Enter the second integer: ");
scanf("%d", &y);

if (x > y)
{
printf("Up");
}
else
{
if (x < y)
{
printf("Down");
}
else
{
if (x = y)
{
printf("Equal") ;
}
else
{
printf("Error") ;
getch();
exit (0);
}
}
}
}

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

[James Hu]

On 2004-09-20, Apotheosis <he************ *@yahoo.com> wrote:

[ code using scanf snipped ]

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

Don't use scanf. Read the answer to question 12.20 in the C-faq
to find out why.

http://www.eskimo.com/~scs/C-faq/top.html

-- James

Dude, you're reading the C-faq!

[CBFalconer]

Apotheosis wrote:

The problem professor gave us is:

Write a program which reads two integer values. If the first is less
than the second, print the message "up". If the second is less than
the first, print the message "down" If the numbers are equal, print
the message "equal" If there is an error reading the data, print a
message containing the word "Error" and perform exit( 0 );

And this is what I wrote:

main()
{
int x;
int y;

printf("Enter the first integer: ");
scanf("%d", &x);

printf("Enter the second integer: ");
scanf("%d", &y);
.... snip ...
Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

Basically you have failed to detect the errors resulting from the
scanf calls. Those are both returning a single value, so they
should be of the form:

if (1 != scanf("%d", &x)) erroraction();
else {
....
}

Never use scanf without checking the return value. Also, main
returns an int. Say so. You should be using:

int main(void)
{
....
return 0;
}

--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!

[Joona I Palaste]

Apotheosis <he************ *@yahoo.com> scribbled the following:

The problem professor gave us is: Write a program which reads two integer values. If the first is less
than the second, print the message "up". If the second is less than
the first, print the message "down" If the numbers are equal, print
the message "equal" If there is an error reading the data, print a
message containing the word "Error" and perform exit( 0 ); And this is what I wrote:
main()
{
int x;
int y; printf("Enter the first integer: ");
scanf("%d", &x); printf("Enter the second integer: ");
scanf("%d", &y); if (x > y)
{
printf("Up");
}
else
{
if (x < y)
{
printf("Down");
}
else
{
if (x = y)
Everyone other failed to spot this. You want == here, not =. = first
assigns y's value to x and then tests if x's value is anything other
than 0. This means that if execution gets this far, any value entered
to y at all, as far as it isn't 0, will print "Equal" regardless of
x's value. Because you already tested for x > y and x < y, this would
otherwise not matter, but it's going to break if you type 0 for both
x and y. In this case your program won't print anything at all.
{
printf("Equal") ;
}
else
{
printf("Error") ;
getch();
exit (0);
}
}
}
}

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"I wish someone we knew would die so we could leave them flowers."
- A 6-year-old girl, upon seeing flowers in a cemetery

[pete]

James Hu wrote:

On 2004-09-20, Apotheosis <he************ *@yahoo.com> wrote:

[ code using scanf snipped ]

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

Don't use scanf. Read the answer to question 12.20 in the C-faq
to find out why.

I disagree.

/* BEGIN new.c */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <ctype.h>

#define LENGTH 100
#define str(x) # x
#define xstr(x) str(x)
#define VSIZE (sizeof variables / sizeof *variables)

int main(void)
{
int x, y, n, rc;
long temp;
char array[LENGTH + 1], *nptr;
struct V {
int *address;
char *string;
} variables[]= {{&x, "first"}, {&y, "second"}};

for (n = 0; VSIZE > n; ++n) {
printf("Enter the %s integer: ", variables[n].string);
fflush(stdout);
rc = scanf("%" xstr(LENGTH) "[^\n]%*[^\n]", array);
if (!feof(stdin)) {
getchar();
}
if (rc != 1) {
puts("Error");
exit(0);
}
nptr = array;
while (isspace(*nptr) ) {
++nptr;
}
if (*nptr == '+' || *nptr == '-') {
++nptr;
}
if (!isdigit(*nptr )) {
puts("Error_2") ;
exit(0);
}
errno = 0;
temp = strtol(array, NULL, 10);
if (errno != 0 || INT_MIN > temp || temp > INT_MAX) {
puts("Error_3") ;
exit(0);
}
*variables[n].address = (int)temp;
}
if (y > x) {
puts("Up");
} else {
if (x > y) {
puts("Down");
} else {
puts("Equal");
}
}
return 0;
}

/* END new.c */
--
pete

[Nicolas Pavlidis]

pete <pf*****@mindsp ring.com> writes:

rc = scanf("%" xstr(LENGTH) "[^\n]%*[^\n]", array);

For portability reasons a propper #define for the linebreak would be
IMHO fine.

Kind regards,
Nicolas
--
| Nicolas Pavlidis | Elvis Presly: |\ |__ |
| Student of SE & KM | "Into the goto" | \|__| |
| pa****@sbox.tug raz.at | ICQ #320057056 | |
|-------------------University of Technology, Graz----------------|

[Felipe Magno de Almeida]

Apotheosis wrote:

The problem professor gave us is:

Write a program which reads two integer values. If the first is less
than the second, print the message "up". If the second is less than
the first, print the message "down" If the numbers are equal, print
the message "equal" If there is an error reading the data, print a
message containing the word "Error" and perform exit( 0 );
And this is what I wrote:

main()
{
int x;
int y;

printf("Enter the first integer: ");
scanf("%d", &x);

printf("Enter the second integer: ");
scanf("%d", &y);

if (x > y)
{
printf("Up");
}
else
{
if (x < y)
{
printf("Down");
}
else
{
if (x = y) here you should replace for x == y {
printf("Equal") ;
}
else
{
printf("Error") ;
getch();
exit (0);
}
}
}
}

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

--
Felipe Magno de Almeida
UIN: 2113442
email: felipe.almeida@ ic unicamp br, felipe.m.almeid a@gmail com
I am a C, modern C++, MFC, ODBC, Windows Services, MAPI developer
from synergy, and Computer Science student from State
University of Campinas(UNICAM P).
To know more about:
Unicamp: http://www.ic.unicamp.br
Synergy: http://www.synergy.com.br
current work: http://www.mintercept.com

[Christopher Benson-Manica]

Apotheosis <he************ *@yahoo.com> spoke thus:

Your indentation is suboptimal, to put it mildly.

main()
main() returns int. You should say so, and must do so under C99.
else
{
if (x = y)
{
printf("Equal") ;
}
else
{
printf("Error") ;
getch();
exit (0);
}
}
}
You are missing a return statement; you must explicitly return an
integer under C89. Notice that your call to exit() does not always
occur.
}

--
Christopher Benson-Manica | I *should* know what I'm talking about - if I
ataru(at)cybers pace.org | don't, I need to know. Flames welcome.

[Edmund Bacon]

he************* @yahoo.com (Apotheosis) writes:

The problem professor gave us is:

Write a program which reads two integer values. If the first is less
than the second, print the message "up". If the second is less than
the first, print the message "down" If the numbers are equal, print
the message "equal" If there is an error reading the data, print a
message containing the word "Error" and perform exit( 0 );
And this is what I wrote:

main()
{
int x;
int y;

printf("Enter the first integer: ");
scanf("%d", &x);

printf("Enter the second integer: ");
scanf("%d", &y);
[ rest of code snipped ]
}
}

Works fine at first, but whenever I enter invalid characters such as
!, A, %, :, etc. It never asks me for the second integer and skip to
printf("Down");
Can anyone be kind enough to explain to me why that happened?

No, but perhaps if you can answer these questions you might figure it
out:

1) what does scanf() do if the input doesn't match the requested
conversion?

2) does scanf have a return value? If so, what is it, and how might
you use that to help you with this problem?

--
Remove -42 for email

[pete]

Nicolas Pavlidis wrote:

pete <pf*****@mindsp ring.com> writes:

rc = scanf("%" xstr(LENGTH) "[^\n]%*[^\n]", array);

For portability reasons a propper #define for the linebreak would be
IMHO fine.

I don't understand what you mean.
Is there something there which is not portable?
What linebreak?

--
pete