Program not running because of "underscore"

Question

I made a program to print an ASCII table up to a certain range (like ASCII from 0 to 104).

#include <stdio.h>

int main(void)
{
    int n;
    printf("\n\nthis program will print list of ASCII values for your computer enter the upper limit for the range - ");
    scanf("%d", &n);

    printf("\nDECIMAL\tCHARACTER");
    for (int i = 0; i <= n; i++)
    {
        printf("\n  %d  |  %c", i, i);
        // printf("\n-------------");
        printf("_");   //when i include this "undescore" it causes problems, the code stops at 27th ASCII character and gets stuck.
    }

    return 0;
}

The 27 decimal corresponds to ASCII SYSTEM CODE - [ESCAPE].

None of the following works, and the code stops at the 27th ASCII character:

printf("__"); //double or multiple underscore does not work.

printf("\n_"); //this doesnt work either.

printf("//_"); //somehow this works.

If I remove that printf("_"); part then the code does not stop at 27 and runs smoothly, the code only stops when I use the underscore (_) character.

If I use a different character (-, *, etc), it runs smoothly.

What can the problem be? Could it be something related to macros?

Edit- when I replaced 'printf("_");' with 'printf("n");' thinking it would perform the same as '\n' some weird language popped up and the language of the terminal changed. when '_' is replaced by 'n'

Escape is the first character of an escape sequence, the actual result depends on the following character(s). In general, you shouldn't try to print control characters in your table. — Barmar, Feb 13 '23 at 17:22
`ESC _` is [APC](https://invisible-island.net/xterm/ctlseqs/ctlseqs.html) which does something weird. Characters with code <32 are control characters and you should not try to print them. — teapot418, Feb 13 '23 at 17:24
For the control character (00..1F, and 7F), you could print (suitably-encoded) Unicode Code Point `0x2400 + i` instead. For example, for 27, this gets you "␛". — ikegami, Feb 13 '23 at 17:24
Suggest changing your loop to `for(int i = 32; i <= n; i++)`. Printing the control characters is not likely to be useful. — Steve Summit, Feb 13 '23 at 17:27
`#include `, then in the `printf()` replace the second `i` with `isprint(i) ? i : ' '`. — John Bayko, Feb 13 '23 at 17:34
it was not that i wanted to print "non printable characters" i was just tinkering around, and something really weird happened when I changed the 'printf("_");' with 'printf("n");' (i thought esc + n was the same as \n and would do the same) instead the language of terminal changed to some other non english text, iam updating the original post with the snapshot. — LearnerK, Feb 14 '23 at 20:57

score 0 · Answer 1 · answered Feb 14 '23 at 00:42

Your terminal support ANSI escape sequences which means it does something with ESC _: Application Program Command. In general, if your printing it, you probably want to make sure it shows up so I am using an alternative format here for non-printable characters:

#include <ctype.h>
#include <stdio.h>

int main(void) {
    printf("\n\nthis program will print list of ASCII values for your computer enter the upper limit for the range - ");
    int n;
    scanf("%d", &n);

    printf("\nDECIMAL\tCHARACTER");
    for (int i = 0; i <= n; i++) {
        if(isprint(i))
            printf("\n  %d  |  %c", i, i);
        else
            printf("\n  %d  | 0x%x", i, i);
        printf("_");
    }
}

Here is a sample output:

 this program will print list of ASCII values for your computer enter the upper limit for the range - 38

DECIMAL CHARACTER
  0  | 0x0_
  1  | 0x1_
  2  | 0x2_
  3  | 0x3_
  4  | 0x4_
  5  | 0x5_
  6  | 0x6_
  7  | 0x7_
  8  | 0x8_
  9  | 0x9_
  10  | 0xa_
  11  | 0xb_
  12  | 0xc_
  13  | 0xd_
  14  | 0xe_
  15  | 0xf_
  16  | 0x10_
  17  | 0x11_
  18  | 0x12_
  19  | 0x13_
  20  | 0x14_
  21  | 0x15_
  22  | 0x16_
  23  | 0x17_
  24  | 0x18_
  25  | 0x19_
  26  | 0x1a_
  27  | 0x1b_
  28  | 0x1c_
  29  | 0x1d_
  30  | 0x1e_
  31  | 0x1f_
  32  |   _
  33  |  !_
  34  |  "_
  35  |  #_
  36  |  $_
  37  |  %_

Program not running because of "underscore"

1 Answers1