/* Program to generate a file called "ascii" containing a
   table of ASCII codes. This requires a computer using ASCII
   codes in order to work correctly. */

/* We use the fact that the first printable ASCII character is
   the space, and the last is '~'.  For other character code
   conventions (such as EBCDIC), this must be changed. */
#define FIRSTCHAR (' ')
#define LASTCHAR ('~')

#include <stdio.h>
#include <stdlib.h>
void create_table(FILE *f);

main() {

    /* Step 1: declare the FILE pointer. */
    FILE *outfile;

    /* Step 2a: attempt to open the file for writing. */
    outfile = fopen("ascii", "w");
        /* Note: first parameter is file name, second is access
                 mode ("w" means "write").  */

    /* Step 2b: check whether we succeeded in opening the file. */
    if (outfile == NULL) {
        printf("ERROR: Could not open file \"ascii\"\n");
        exit(EXIT_FAILURE);
    }

    /* (Here we are sure the file is open for writing.)
       Step 3: Write all required information to the file. */
    create_table(outfile);

    /* Step 4: close the file. */
    fclose(outfile);

    /* At this point, the completed file should exist on the disk. */
    return 0;
}

/******* create_table ********
 Creates a table showing ASCII codes for all printable characters
 in five columns, with headings.
 On Entry: 'outfile' must refer to a file correctly opened for output.
           The file must not end with a partially-complete output line.
 On Exit:  The table will be appended to the file, which is still open.
*/

void create_table(FILE * outfile) {
    int ch, i;

    /* Heading */
    fprintf (
        outfile,
        "char code  char code  char code  char code  char code\n"
        "==== ====  ==== ====  ==== ====  ==== ====  ==== ====\n"
    );

    /* Detail lines.  'ch' is the character code, i is the number
       printed so far (used to break lines every five characters.
    */
    i = 0;
    for (ch=FIRSTCHAR; ch<=LASTCHAR; ch++) {
        fprintf(outfile, " '%c' %3d", ch, ch);   /* write char and code */
        i++;                                     /* That's one more! */
        if (i % 5 == 0) {                        /* Even multiple of 5 */
            putc('\n', outfile);                 /* Puts a single char */
        } else {
            fputs("   ", outfile);               /* Puts a string */
        }
    }
    putc('\n', outfile);         /* Ensure final line complete */
}