Converting all strings in a txt file to lowercase in c

I am assigned to convert all strings to lowercase in a txt file and then output it in a new txt file but i cant seem find anywhere how to do it. Any help would be very appriciated! Thank you This is what i have till now but there is the y at the end so im thinking if there is a better way to do it or if i can remove the y with the two dots on top..

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

void main() {
   FILE *fp1, *fp2;
   char a;

   fp1 = fopen("test.txt", "r");
   if (fp1 == NULL) 
   {
      puts("cannot open this file");
      exit(1);
   }

   fp2 = fopen("test1.txt", "w");
   if (fp2 == NULL) {
      puts("Not able to open this file");
      fclose(fp1);
      exit(1);
   }

   do
   {
      a = fgetc(fp1);
      a = tolower(a);
      fputc(a, fp2);
   } while (a != EOF);

   fcloseall();
   getch();
}

Solution

When you read input from a file, you should always check whether you get valid input before proceeding to use it. In your case, you get input in the line.

a = fgetc(fp1);

You need to check whether a is valid input before proceeding to use it.

if ( a != EOF )
{
   a = tolower(a);
   fputc(a, fp2);
}

Another thing to update. Don't use

char c;

Use

int c;

instead.

char type can be a signed type or unsigned type on your platform. If it is an unsigned type, it will never have a negative value. Hence, it will never equal EOF, which is -1 often, which will lead to an infinite loop.

If you lookup the documentation of fgetc, you will notice that its return type is int, not char.

Your program can be updated to something like:

void main() {
   FILE *fp1, *fp2;
   int a;

   // Add rest of your code
   // ...

   do
   {
      a = fgetc(fp1);
      if ( a != EOF )
      {
         a = tolower(a);
         fputc(a, fp2);
      }
   } while (a != EOF);

   // Add rest of your code
   // ...
}

The do-while loop can be simplified to:

   while ( (a = fgetc(fp1)) != EOF )
   {
      a = tolower(a);
      fputc(a, fp2);
   }