From: Martin Ambuhl <mambuhl AT earthlink DOT net>
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Newsgroups: comp.os.msdos.djgpp
Subject: Re: Simple program.  Strange results.
References: <HfZ2b.3213$cQ1 DOT 755278 AT kent DOT svc DOT tds DOT net>
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Date: Wed, 27 Aug 2003 10:33:49 GMT
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Kenton W. Mellott wrote:

> When compiling the following program with gcc (no switches) almost all the
> input variable end up displaying strange results.
> 
> 
>         #include <stdio.h>
> 
>         int scanf(const char *format, ...);

Don't do this.  Trust <stdio.h> to have the correct prototype.

> 
>         int main()
>         {
>                 puts("Please enter a string.");
>                 char buf[100];
>                 scanf("%s", buf);
>                             printf("you just entered: ''%s''.  \n", buf );
> 
> 
>                 puts("Please enter a floating point number.");
>                 float x,y;
>                 scanf("%f", !x);
                               ^^^
The '!' is wrong.  You mean `scanf("%f", &x);'

>                             printf("you just entered: '%g'.  \n", !x );
                                                                     ^^^
The '!' is wrong.  You mean `printf("you just entered: '%g'.\n", x);

> 
> 
>                 puts("Please enter 2 floating point numbers and a string.");
>                 scanf("%f %f %s", !x, !y, buf);
>                             printf("you just entered: '%g','%g', '%s'.\n",
> !x, !y, buf);

As before, all the '!'s are wrong.

> 
> 
>  }

Please use spaces instead of tabs when preparing code for posting.  You can 
see above what a mess you got.

Here's a version that is better formatted, will compile under either C89 or 
C99 (as well as gnu89 and gnu99), and takes "enter a string" more seriously:

#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main()
{
     char buf[100], *nl;
     float x, y;
     int nchar;
     puts("Please enter a string.");
     fgets(buf, sizeof buf, stdin);
     if ((nl = strchr(buf, '\n')))
         *nl = 0;
     printf("you just entered: \"%s\".\n", buf);


     puts("Please enter a floating point number.");
     fgets(buf, sizeof buf, stdin);
     sscanf(buf, "%f", &x);
     printf("you just entered: '%g'.\n", x);


     puts("Please enter 2 floating point numbers and a string.");
     fgets(buf, sizeof buf, stdin);
     if ((nl = strchr(buf, '\n')))
         *nl = 0;
     sscanf(buf, "%f %f %n", &x, &y, &nchar);
     printf("you just entered: '%g','%g', \"%s\".\n", x, y, buf + nchar);
     return 0;
}







-- 
Martin Ambuhl