PLEASE HELP!

[coinjo]

#include<fstrea m>
using namespace std;

int main()
{
ifstream indata;
ofstream outdata;

indata.open("D: \\C++\\New Folder\\infile. txt");
outdata.open("D :\\C++\\New Folder\\outfile .txt");

int a=0;
int i=0;
int b=0;

while(a<9)
{
indata>>i;
b=i;
outdata<<b<<" ";
a=a+1;
}
indata.close();
outdata.close() ;

return 0;

}

This is in the infile.txt

1
2
3
4
5
6
7
8
9

The infile.txt and the outfile.txt are both in the same folder but when
i run the program even after deleting the outfile.txt it shows this:
0 0 0 0 0 0 0 0 0

rather than this:
1 2 3 4 5 6 7 8 9

PLEASE HELP!

[mlimber]

Re: PLEASE HELP!

coinjo wrote:[color=blue]
> #include<fstrea m>
> using namespace std;
>
> int main()
> {
> ifstream indata;
> ofstream outdata;
>
> indata.open("D: \\C++\\New Folder\\infile. txt");
> outdata.open("D :\\C++\\New Folder\\outfile .txt");[/color]

Prefer to open with the constructors:

ifstream indata( "in.txt" );
ofstream outdata( "out.txt" );

Note that you didn't check if the open succeeded, and I'm guessing
that's your problem (perhaps because of the space in the pathname).
[color=blue]
>
> int a=0;
> int i=0;
> int b=0;[/color]

Don't declare variables until you use them. i and b should be declared
inside the loop. (Actually, you don't need both of them in the first
place.)
[color=blue]
>
> while(a<9)
> {
> indata>>i;
> b=i;
> outdata<<b<<" ";
> a=a+1;[/color]

"++a;" is more conventional. Even better would be a for loop rather
than a while loop.
[color=blue]
> }[/color]

You need to check for read failures (due to disk errors, end of file,
etc.). Prefer the canonical form:

while( indata >> i )
{
outdata << i << ' ';
}

You could put a check for the iteration cound in the while condition if
the input file could have more than 9 pieces of data and you only want
the first 9 of them:

while( (indata >> i) && (a++ < 9) )
{
outdata << i << ' ';
}
[color=blue]
> indata.close();
> outdata.close() ;[/color]
[snip]

Unnecessary. The destructors do this automatically. You should
generally only use close when you need to close the file before the end
of scope.


Cheers! --M

[Pep]

Re: PLEASE HELP!

mlimber wrote:
[color=blue]
> coinjo wrote:[color=green]
>> #include<fstrea m>
>> using namespace std;
>>
>> int main()
>> {
>> ifstream indata;
>> ofstream outdata;
>>
>> indata.open("D: \\C++\\New Folder\\infile. txt");
>> outdata.open("D :\\C++\\New Folder\\outfile .txt");[/color]
>
> Prefer to open with the constructors:
>
> ifstream indata( "in.txt" );
> ofstream outdata( "out.txt" );
>
> Note that you didn't check if the open succeeded, and I'm guessing
> that's your problem (perhaps because of the space in the pathname).
>[color=green]
>>
>> int a=0;
>> int i=0;
>> int b=0;[/color]
>
> Don't declare variables until you use them. i and b should be declared
> inside the loop. (Actually, you don't need both of them in the first
> place.)
>[color=green]
>>
>> while(a<9)
>> {
>> indata>>i;
>> b=i;
>> outdata<<b<<" ";
>> a=a+1;[/color]
>
> "++a;" is more conventional. Even better would be a for loop rather
> than a while loop.
>[color=green]
>> }[/color]
>
> You need to check for read failures (due to disk errors, end of file,
> etc.). Prefer the canonical form:
>
> while( indata >> i )
> {
> outdata << i << ' ';
> }
>
> You could put a check for the iteration cound in the while condition if
> the input file could have more than 9 pieces of data and you only want
> the first 9 of them:
>
> while( (indata >> i) && (a++ < 9) )
> {
> outdata << i << ' ';
> }
>[color=green]
>> indata.close();
>> outdata.close() ;[/color]
> [snip]
>
> Unnecessary. The destructors do this automatically. You should
> generally only use close when you need to close the file before the end
> of scope.
>
>
> Cheers! --M[/color]

I would agree with this. Initially I thought this might be a problem local
to windows as I ran the program on linux and had no problems with it. Then
I ran on windows with no problems until I deleted the input file.

Ho hum.