Splitting long line using two fprintf doesn't display proper output

[Guti14]

The program writes a number to a text file correctly if it is a prime number, but it doesn't if the number is not prime. Well, it knows that it is not prime, but it doesn't display the correct highest divisor, always just 0.
I think it has to do that I used fprintf twice, because it does work if I put it all on one line, but then it exceeds the page margins.
Would anyone know a way around this problem?

#define LinesPerScreen 12

#include <stdio.h>
#include <process.h>      
#include <conio.h>        

int write_prime_numbers();
int read_prime_numbers();

int main()
{
   int reply = 0;
   int items = 3;

   clrscr();
   printf("Welcome to PRIME NUMBER program");
   while (reply < items)
   {
      printf("\n\nChoose from the following menu: ");
      printf("\nSelect %d to write data to a text disk file", 1);
      printf("\nSelect %d to read data from a text disk file", 2);
      printf("\nSelect %d or a higher number to exit from the program", items);
      printf("\nYour choice: ");
      scanf("%d", &reply);

      if (reply == 1)
      {
         write_prime_numbers();
      }
      if (reply == 2)
      {
         read_prime_numbers();
      }
      if (reply < 1)
      {
         printf("\nChoice %d out of range. Type in 1 or 2 or a higher number.");
      }
   }
   printf ("\n\nThank you for using this program.\n");
   getch();
   return 0;
}

int write_prime_numbers()
{
   FILE *write_prime_file;
   int number, i, remainder;
   int not_divisible = 1;
   int biggest = 1;
   char reply;
   int rec_no = 0;
   write_prime_file = fopen ("prime_io.txt", "w");
   fprintf(write_prime_file, "This is the content of your text file.\n");
   fprintf(write_prime_file, "-1 indicates user typed in terminating value.\n");
   while ( number != -1)
   {
      printf("\n\nCollecting data for the file Record Number %d\n", rec_no);
      printf("\nEnter a number to see if its prime(e.g. 1990) OR\n");
      printf("Enter -1 to quit writing to a text file and return to the main");
      printf(" menu\n");
      printf("Your choice: ");
      scanf("%d", &number);
         for( i = 2; i < number - 1; i++ )
         {
            remainder = number % i;
            if(remainder == 0 )
            {
               not_divisible = 0;
               biggest = i;
            }
         }

         if(not_divisible == 1)
         {
         fprintf(write_prime_file, "\nThe number %d is a prime number", number);
         }
         else
         {
       fprintf(write_prime_file, "\nThis number's highest divisor is %d");
         fprintf(write_prime_file, " and thus is not prime", biggest);
         }
   }

   fclose(write_prime_file);
   return 0;
}

int read_prime_numbers()
{
   FILE *read_prime_file;
   char content_in[60];
   int rec_no = 0;
   printf ("\nInside of read a record function\n");
   read_prime_file = fopen ("prime_io.txt", "r");
   while (!feof(read_prime_file))
   {
      fgets (content_in, 60, read_prime_file);
      printf (content_in);
      if (rec_no >= LinesPerScreen)
      {
         printf ("\n");
         getch();
         return 0;
      }
   }
   fclose(read_prime_file);
}

[JarJarBinks]

fprintf(write_prime_file, "\nThis number's highest divisor is %d");
fprintf(write_prime_file, " and thus is not prime", biggest);

it can go past the page margins without a problem
you can write your whole program in one line,
the c/c++ compiler will not care, but you could try this

fprintf(write_prime_file, "\nThis number's highest divisor is %d", biggest);
fprintf(write_prime_file, " and thus is not prime");

I did not compile your code or check to see if that fixed your
problems its just an item i noticed, if your still having a problem
i may compile your code and see what me thinks!

[Guti14]

Yes, thanks, this worked, though in Borland C++ Builder 6, it still exceeds the margin by 5 characters.

Another problem I have though is, when the user enters the "sentinal value"(-1), it is also written to the txt file, and the program prints the same output for this value as the last "proper" value entered in. So when I entered in 8 as my last value, it doesn't just display 4 is the highest divisor for value 8, but also for -1.

I tried using something like, would you like to enter another number? and the user had to enter 'n' || 'N' or 'y' || 'Y' but when the user entered in any other letter than n or N, the program would prompt for a new number anyway.

Would you know any better methods?

[JarJarBinks]

fprintf(write_prime_file, "This is the content of your text file.\n");
fprintf(write_prime_file, "-1 indicates user typed in terminating value.\n");

im not sure but i think you ment for this to be :

printf("This is the content of your text file.\n");
printf("-1 indicates user typed in terminating value.\n");

as for it exceeding the margin, you could move more of the first
content from the first fprintf, to the 2nd fprintf, but if you move
then %d, make sure you mvoe your variable to the 2nd fprintf.


for the problem with prompting for a new number, perhaps
you could simply :

bool quit = false;
while(quit == false)
{
     int mynumber;
     cout << "Please enter a number? :  ";
     cin >> mynumber;

     //do stuff here



     char newnumber;
     cout << "Would you like to enter a new number?  : ";
     cin >> newnumber;

     if(newnumber == 'n' || newnumber == 'N')
     {
            quit == true;
     }
}
return 0;

[Salem]

You can also do this, since the compiler will join adjacent strings for you.

fprintf(write_prime_file, "This number's highest divisor is %d"
                          " and thus is not prime\n", biggest);

By the way, put the newline at the end, not the start of the line.
Otherwise your file ends up with a blank line at the start, and no newline at the end.

> Another problem I have though is, when the user enters the "sentinal value"(-1), it is also written to the txt file,
Check the value you input then

scanf("%d", &number);
if ( number == -1 ) break;

> while (!feof(read_prime_file)) {
> fgets (content_in, 60, read_prime_file);
> printf (content_in);
Bad for two reasons
1. The feof() is discussed in the FAQ
2. NEVER call printf with a control string you read from the outside world. All anyone has to do is put a % character in there and then your code is off converting non-existent parameters.

   while (fgets (content_in, sizeof content_in, read_prime_file)) {
      fputs(content_in,stdout);

Using sizeof instead of the literal value 60 means you have one less thing to change if you decide on a different buffer size.