Showing problem

[beginner10]

How can i changhe this code showing how many persons i saved to the file?
And it prints pretty much rubbish. Where is the problem?

#include <stdio.h>
int main()
{
int i;
FILE *data_file;
char list[] = "list.txt";

struct person {
char firstname[20];
char lastname[25];
int phonenumber;

};

struct person person_list[50];

for(i=0; i<1; i++) {

printf("Give your firstname:");
scanf("%s", person_list[i].firstname);

printf("Give your lastname:");
scanf("%s", person_list[i].lastname);

printf("Give your phone number:");
scanf("%d", &person_list[i].phonenumber);

}

if ((data_file = fopen(list, "w")) == NULL) {
printf("Error opening file");
return 0;
} else {

for(i=0; i<=2; i++)
{
fprintf(data_fi le, "%s %s %d\n", person_list[i].firstname,
person_list[i].lastname, person_list[i].phonenumber);
}
}
fclose(data_fil e);
printf("Data saved succesfully!");
return 0;
}

[Shan]

The problem is with your design itself. You declared an array of 50
like

struct person person_list[50]; but in the following statement you are looping for only one person's
input:
for(i=0; i<1; i++) {

printf("Give your firstname:");
scanf("%s", person_list[i].firstname);

printf("Give your lastname:");
scanf("%s", person_list[i].lastname);

printf("Give your phone number:");
scanf("%d", &person_list[i].phonenumber);

}
For printing to the file you are printing for two persons likefor(i=0; i<=2; i++)
{
fprintf(data_fi le, "%s %s %d\n", person_list[i].firstname,
person_list[i].lastname, person_list[i].phonenumber);
}
}

The solution is
1) Get input for as many persons you want but lesser than the array
length.
2) write the data to the file,.
3) For the above two steps you have to change the for loop to
accomodate the array length.
4) Read the file back and check for the number of lines before you
encounter EOF.

-Shan

[Jens.Toerring]

beginner10 <pe************ @yahoo.com> wrote:

How can i changhe this code showing how many persons i saved to the file?
And it prints pretty much rubbish. Where is the problem? #include <stdio.h>
int main()
int main( void )
{
int i;
FILE *data_file;
char list[] = "list.txt";

struct person {
char firstname[20];
Using 'magic' numbers like this is problematic. Better use a define at
the start of the program like

#define MAX_FIRST_NAME_ LENGTH 20

and stick with that, so you only need to change it in a single place
when you later realize that 19 characters isn't enough to store all
first names.
char lastname[25];
int phonenumber; };

struct person person_list[50];
Again, I would recommend to use

#define MAX_PERSONS 50

instead of a fixed number.

for(i=0; i<1; i++) {
Why would you stop here once 'i' is 1? Wouldn't it make more sense
to bail out of the loop if 'i' is 50 or the user enters something
from which you can deduce that (s)he doesn't want to enter more data
(like an empty line for the first name)?
printf("Give your firstname:");
scanf("%s", person_list[i].firstname);
Let's hope there's no-one with a space in the name, otherwise using
scanf() like that won't work (hint: scanf() stops at white-space
characters when reading in strings with "%s"). And moreover, better
hope that there's no-one with a first name that's longer than 19
characters or you write past the end of the array. As a way to
correct both problems look up the fgets() function.
printf("Give your lastname:");
scanf("%s", person_list[i].lastname); printf("Give your phone number:");
scanf("%d", &person_list[i].phonenumber);
Using scanf() here is is going to be a problem if the user makes a
typo and enters an non-digit (maybe just a space). Again, look up
fgets() and check the buffer you get from it for something that can
be interpreted as a phone number.
}

if ((data_file = fopen(list, "w")) == NULL) {
printf("Error opening file");
return 0;
} else {
Actually, no 'else' is needed here - when opening the file failed you
already exited the program.
for(i=0; i<=2; i++)
Since you stop above when 'i' is 1 you never have more than a single
person in your list, Why would you try to write out now 3 sets of
data records? Better keep count how many people got entered by the
user and than write out as many records.
{
fprintf(data_fi le, "%s %s %d\n", person_list[i].firstname,
person_list[i].lastname, person_list[i].phonenumber);
}
}
fclose(data_fil e);
printf("Data saved succesfully!");
return 0;
}

Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de

[Neo]

"beginner10 " <pe************ @yahoo.com> wrote in message
news:d9******** *************** *******@localho st.talkaboutpro gramming.com...

How can i changhe this code showing how many persons i saved to the file?
And it prints pretty much rubbish. Where is the problem?

#include <stdio.h>
int main()
{
int i;
FILE *data_file;
char list[] = "list.txt";

struct person {
char firstname[20];
char lastname[25];
int phonenumber;
better to use char array for phonenumber field too....
lets say user input something like : 9899325025
then it will overflow and store wrong information.
by using char array you have more precise control
over how many digits you want to store in phonenumber
field.


};

struct person person_list[50];
Oops! use #defines instead of magic numbers....
like #define MAX_RECORDS 50

for(i=0; i<1; i++) {

printf("Give your firstname:");
scanf("%s", person_list[i].firstname);

printf("Give your lastname:");
scanf("%s", person_list[i].lastname);

printf("Give your phone number:");
scanf("%d", &person_list[i].phonenumber);

}

if ((data_file = fopen(list, "w")) == NULL) {
printf("Error opening file");
return 0;
} else {

for(i=0; i<=2; i++)
{
you have valid data only in first record, but here you are accessing
and storing second and third row also... that contains garbage.
either properly initialize the whole array in the begining of the program
if you want to store more records then input from the user.
or better keep this loop counter same as above.

Hope this will help U....

-Neo
fprintf(data_fi le, "%s %s %d\n", person_list[i].firstname,
person_list[i].lastname, person_list[i].phonenumber);
}
}
fclose(data_fil e);
printf("Data saved succesfully!");
return 0;
}

[beginner10]

I'm still doesn't understood this? Sorry.

[beginner10]

I'm still doesn't understood this? Sorry.

[dandelion]

"beginner10 " <pe************ @yahoo.com> wrote in message
news:56******** *************** *******@localho st.talkaboutpro gramming.com...

I'm still doesn't understood this? Sorry.

I think he means that if you have 25 persons, they will probably have 25
phonenumbers, too.

[Mike Wahler]

"beginner10 " <pe************ @yahoo.com> wrote in message
news:88******** *************** *******@localho st.talkaboutpro gramming.com...

I'm still doesn't understood this? Sorry.
Please don't drop attributions and context. See below.

"Neo" <ti************ ***@yahoo.com> wrote in message
news:33******** *****@individua l.net...
"beginner10 " <pe************ @yahoo.com> wrote in message

news:d9******** *************** *******@localho st.talkaboutpro gramming.com...

How can i changhe this code showing how many persons i saved to the file? And it prints pretty much rubbish. Where is the problem?

#include <stdio.h>
int main()
{
int i;
FILE *data_file;
char list[] = "list.txt";

struct person {
char firstname[20];
char lastname[25];
int phonenumber;

better to use char array for phonenumber field too....
lets say user input something like : 9899325025
then it will overflow and store wrong information.
by using char array you have more precise control
over how many digits you want to store in phonenumber
field.

What he means is that you're only guaranteed (by the
language standard) a range of values for type 'int' from
-32767 to 32767 inclusive. Attempts to store a value outside
the range of a signed integer type will produce undefined
behavior.

Of course many implementations provide a type 'int' with
a much larger range, but you should still provide protection
against overflow/underflow. If you want your code to be
maximally portable, don't assume 'int' can store less than
-32767 or greater than 32767.

I agree with Neo that an array of char would be better and
more flexible. But you still need to remember to protect
against overflowing your array.

-Mike

[Robert B. Clark]

On Mon, 03 Jan 2005 06:36:42 -0500, "beginner10 "
<pe************ @yahoo.com> wrote:

How can i changhe this code showing how many persons i saved to the file?
And it prints pretty much rubbish. Where is the problem?

#include <stdio.h>
int main()
int main(void)
{
int i;
FILE *data_file;
char list[] = "list.txt";

struct person {
char firstname[20];
char lastname[25];
int phonenumber;
This is a poor choice of data type for phonenumber. See below.

};

struct person person_list[50];
Quick note: Do avoid using "magic constants." Instead, use macros with
meaningful names, e.g.,

#define FNAME_LEN 20
#define LNAME_LEN 25
#define PHONENUM_LEN 7
#define MAX_PERSON_LIST 50

struct person
{
char firstname[FNAME_LEN];
char lastname[LNAME_LEN];
char phonenumber[PHONENUM_LEN]
};

struct person person_list[MAX_PERSON_LIST];

The advantage is the code is easier to read and maintain. What if you
later decided to store the entire 11-digit phone number? All you need
do is edit the PHONENUM_LEN macro definition and recompile, instead of
searching your entire code for occurrences of "7."

for(i=0; i<1; i++) {
This loop will execute only ONCE.

printf("Give your firstname:");
scanf("%s", person_list[i].firstname);
This will break if whitespace is part of the name--scanf stops scanning.

This will break if the user enters more than 19 characters for the
name--scanf will happily allow one to overflow buffers.

Use fgets instead of scanf for more robust data entry.
printf("Give your lastname:");
scanf("%s", person_list[i].lastname);

printf("Give your phone number:");
scanf("%d", &person_list[i].phonenumber);
A telephone number may not necessarily be represented as an integer.
Even if it were, the degree of precision on a given platform may still
make an integer a poor choice for a phone number.

What if the phone number were 9991212? On many platforms, this number
will overflow a signed int.

Result: Potential (probable) rubbish.

Consider using a string instead.
}

if ((data_file = fopen(list, "w")) == NULL) {
printf("Error opening file");
return 0;
} else {

for(i=0; i<=2; i++)
This loop will execute three times, but you still only have ONE
populated person_list[] array index--see the previous for loop.

The remaining 49 person_list[] indices are full of uninitialized,
unpredictable garbage.

Result: Definitely rubbish, as you are now dancing on the head of the UB
daemon. With cleats on.
{
fprintf(data_fi le, "%s %s %d\n", person_list[i].firstname,
person_list[i].lastname, person_list[i].phonenumber);
}
}
fclose(data_fil e);
printf("Data saved succesfully!");
return 0;
}

You'll still want some way to determine when to stop adding entries to
your person_list[] array, won't you? You will also want to be able to
read your newly-created data file and display the entries within it.
--
Robert B. Clark (email ROT13'ed)
Visit ClarkWehyr Enterprises On-Line at http://www.3clarks.com/ClarkWehyr/

[Mark McIntyre]

On Mon, 03 Jan 2005 13:06:26 -0500, in comp.lang.c , Robert B. Clark
<ep****@3pynexf .pbz> wrote:

On Mon, 03 Jan 2005 06:36:42 -0500, "beginner10 "
<pe*********** *@yahoo.com> wrote:

int phonenumber;

This is a poor choice of data type for phonenumber. See below.

Depends - many company internal switchboards can handle up to 9999 numbers.
Int works for that.

--
Mark McIntyre
CLC FAQ <http://www.eskimo.com/~scs/C-faq/top.html>
CLC readme: <http://www.ungerhu.com/jxh/clc.welcome.txt >

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