Question

I want to just create a small encryption program, i want to read characters from a file and just add the current value of i to the characters and store it in a new file.

example : abcd should be stored as aceg

Here is the code snippet:

main()
{
   int i=0,c;
   char filename[30],o_filename[30];
   FILE *file,*outfile;
   printf("\nEnter filename:");
   scanf("%s",&filename);
   printf("\nEnter output filename : ");
   scanf("%s",&o_filename);
   if( ( (file = fopen(filename,"a"))==NULL) || ((outfile = fopen(o_filename,"a+"))==NULL))
   printf("\nERROR - Cannot proceed");
   else
   {
       c = 0;
       while(c!=-1)
       {
                   c = getc(file);
                   putc((c+i),outfile);
                   i++;
       }
       printf("\nEncryption Successful!\n");
    }
    getch();
}

What’s the bug with the above program?

Answer 1

Th function getc returns an int, not a char. EOF cannot be represented in a char.

Change the type of c to int and test against EOF in the loop.

EDIT

To correct the off by one error spotted by marc you could try this idiom:

while ((c = getc(file)) != EOF)