Thread: Mysterious number is being printed.

Originally Posted by laserlight

You do not show what is CHECK, CHECKBORDER, number and CHECKFORMAT, so all I can say is that there is a bug in your code

Sorry here are the definitions of what those defines are:

Code:

#define CHECK         "************************************************************\n"
#define CHECKBORDER   "*                                    Check No. %3d         *\n"
#define CHECKFORMAT   "*                                                          *\n"

They are defines that make up the description and formatting of the check I am supposed to write with my program

Originally Posted by laserlight

Post the smallest and simplest compilable program that demonstrates the problem.

Okay I believe that this would be the shortest code that would compile.

Code:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
void printReport( FILE **inputFILE);

#define CHECK         "************************************************************\n"
#define CHECKBORDER   "*                                    Check No. %3d         *\n"
#define CHECKFORMAT   "*                                                          *\n"

 
int number;

FILE * inputFILE;
printReport(&inputFILE);

fprintf(stdout, CHECK);
fprintf(stdout, CHECKBORDER, number);
fprintf(stdout,CHECKFORMAT);
fclose(inputFILE);




void printReport( FILE **inputFILE)
{
  *inputFILE=fopen("./check.txt","r");
  if(*inputFILE==NULL)
  { 
    printf("File cannot be accessed");
    exit(-80);
  }
}

Originally Posted by laserlight

Where's the main function?

Code:

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
void printReport( FILE **inputFILE);

#define CHECK         "************************************************************\n"
#define CHECKBORDER   "*                                    Check No. %3d         *\n"
#define CHECKFORMAT   "*                                                          *\n"

int main(void)
{
   int number;

   FILE * inputFILE;
   printReport(&inputFILE);

   fprintf(stdout, CHECK);
   fprintf(stdout, CHECKBORDER, number);
   fprintf(stdout,CHECKFORMAT);
   fclose(inputFILE);
}




void printReport( FILE **inputFILE)
{
  *inputFILE=fopen("./check.txt","r");
  if(*inputFILE==NULL)
  { 
    printf("File cannot be accessed");
    exit(-80);
  }
}

You have a warning:

Code:

C:\Users\Josh2\Documents\sandboxc\main.c||In function 'main':|
C:\Users\Josh2\Documents\sandboxc\main.c|18|warning: 'number' is used uninitialized in this function [-Wuninitialized]|
||=== Build finished: 0 errors, 1 warnings (0 minutes, 0 seconds) ===|

Mind you I had to wrap lines 11 - 20 in a main function to get it to compile.

Originally Posted by whiteflags

You have a warning:

Code:

C:\Users\Josh2\Documents\sandboxc\main.c||In function 'main':|
C:\Users\Josh2\Documents\sandboxc\main.c|18|warning: 'number' is used uninitialized in this function [-Wuninitialized]|
||=== Build finished: 0 errors, 1 warnings (0 minutes, 0 seconds) ===|

Mind you I had to wrap lines 11 - 20 in a main function to get it to compile.

I didn't get that warning, but at first it printed 2 then I thought it was because i hadn't initialized it so I did then it printed 0 after i initialized it to 0.

I didn't get that warning,

That's a problem. I have my warnings set to the highest possible level off complaint. I ask my compiler to complain about nearly everything it can. Doing this helps me explain problems like yours. Watch.

but at first it printed 2 then I thought it was because i hadn't initialized it so I did then it printed 0 after i initialized it to 0.

Yeah using variables before they are set to a value has unpredictable results. These unpredictable results are called undefined behavior, and variables that haven't been set a value are uninitialized. Local variables will not be automatically initialized in C.

Part of the reason C99 made it possible to define variables in mixed code is because in older standards, declaring variables bare like you have done was common and unfortunately forgetting to set a value was also a common mistake. Payign attention to warnings is one way to fix it. The other way to fix it was to declare locals as close to where they are used as possible. Which again C99 made possible. I mention C99 because you should be learning it, and in my experience, people learn it somewhat secretly. They aren't told that // comments are a C99 feature for example. Heaven help them if they also compile C as C++.

Originally Posted by laserlight

Okay, so what's the problem now? Printing 0 looks correct if you initialise number to 0.

I thought it wasn't supposed to print 0 if you only initialize it. Also, won't that create a problem in the future for me because the number that is supposed to go in there is 100 then increment to 105.


I'm over thinking everything aren't I?