How to draw a circle?

Question

So, I wrote a little code to display to draw circles. It kinda works, but in a really janky way. This is the output of running the program and inputting 6:

 O       O
O         O
           O
           O
           O
           O
           O
           O
           O
O         O
 O       O
  OOOOOOO

Not looking great.

#include <stdio.h>
#include <math.h>
int main()
{
    int num, dist, x, y;
    printf("Enter the Radius of the Circle: ");
    scanf_s("%d", &num);
    {
        for (x = 1; x <= num * 2; x++)
        {
            for (y = 1; y <= num * 2; y++)
            {
                dist = sqrt((x - num) * (x - num) + (y - num) * (y - num));
                {
                    if (dist==num)
                    {
                        printf("O");
                    }
                    else
                    {
                        printf(" ");
                    }
                }

            }
            printf("\n");

        }

    }
    return 0;
}

This is the code, searched around the web for answers, it might be the placement of the "new line" code. Tried different spots, nope.

Answer 1

I wrote one once, but mine just uses summations and subtractions, no multiplications (except one square, at the beginning) using The Bresenham Algorithm. Here is the code. (you can get it also from github)

/* bresenham.c -- program to draw ASCII circles with Bresenham's algorithm.
 * Author: Luis Colorado <luicoloradourcola@gmail.com>
 * Date: Wed Jan 11 10:50:17 EET 2017
 * Disclaimer: (C) 2017 LUIS COLORADO. ALL RIGHTS RESERVED.
 * BSD 3-Clause License
 * 
 * Copyright (c) 2017, Luis Colorado
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 * 
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 * 
 * * Neither the name of the copyright holder nor the names of its
 *   contributors may be used to endorse or promote products derived from
 *   this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <errno.h>
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <unistd.h>

#define FL_FILL     (1 << 0)
#define FL_TRACE    (1 << 1)

#define F(x) "%s:%d:%s: " x, __FILE__, __LINE__, __func__

/* draws a horizontal line at row y, between x1 and x2 */
static void hline(int x1, int x2, int y)
{
    static char theLine[] =
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************"
    "*****************************************";
#define THE_LINE_LENGTH (sizeof theLine - 1)
    int count = (x2 - x1 + 1) << 1;

    printf("\033[%d;%dH", y, x1<<1);
    while (count >= THE_LINE_LENGTH) {
        fputs(theLine, stdout);
        count -= THE_LINE_LENGTH;
    } /* while */
    printf("%.*s", count, theLine);
} /* hline */

/* draws a dot at coordinates (x, y) */
static void dot(int x, int y)
{
    printf("\033[%d;%dH*", y, x<<1);
} /* dot */

/* draws a circle of radius r and center at (cx, cy) */
void bh(int r, int cx, int cy, int flags)
{
    int r2 = r*r + r;
    int x = 0, x2 = 0, dx2 = 1;
    int y = r, y2 = y*y, dy2 = 2*y - 1;
    int sum = r2;

    while(x <= y) {
        if (flags & FL_TRACE) {
            printf(F("x=%3d, x2=%5d, dx2=%3d, y=%3d, y2=%5d, dy2=%3d, sum=%5d\n"),
                x, x2, dx2, y, y2, dy2, sum);
        } else {
            if (flags & FL_FILL) {
                       hline(cx - y, cx + y, cy + x);
                if (x) hline(cx - y, cx + y, cy - x);
            } else {
                             dot(cx - y, cy + x); if (y) dot(cx + y, cy + x);
                    if (x) { dot(cx - y, cy - x); if (y) dot(cx + y, cy - x); }
                if (x != y) {
                             dot(cx - x, cy - y); if (x) dot(cx + x, cy - y);
                    if (y) { dot(cx - x, cy + y); if (x) dot(cx + x, cy + y); }
                }
            } /* if */
        } /* if */

        sum -= dx2;
        if (sum <= y2) {
            if (!(flags & FL_TRACE) && (flags & FL_FILL) && (x != y)) {
                       hline(cx - x, cx + x, cy - y);
                if (y) hline(cx - x, cx + x, cy + y);
            } /* if */
            y--; y2 -= dy2; dy2 -= 2;
        } /* if */
        x++;
        x2 += dx2;
        dx2 += 2;
    } /* while */
} /* bh */

int main(int argc, char **argv)
{
    int i;
    char *cols = getenv("COLUMNS");
    char *lines = getenv("LINES");
    int cx, cy;
    int opt;
    int flags = 0;

    while ((opt = getopt(argc, argv, "fv")) != EOF) {
        switch(opt) {
        case 'f': flags |= FL_FILL; break;
        case 'v': flags |= FL_TRACE; break;
        } /* switch */
    } /* while */

    argc -= optind;
    argv += optind;

    if (cols && lines) {
        cx = atoi(cols);
        cy = atoi(lines);
    } else { /* try to get from tty */
        struct winsize win;
        int res = ioctl(0, TIOCGWINSZ, &win);
        if (res == 0) {
            cx = win.ws_col;
            cy = win.ws_row;
        } else {
            fprintf(stderr,
                F("TIOCGWINSZ: %s (errno=%d)\n"),
                strerror(errno), errno);
            cx = 80; cy = 24;
        } /* if */
    } /* if */

    /* center coordinates */
    cx /= 4;
    cy /= 2;

    if (!(flags & FL_TRACE))
        fputs("\033[2J", stdout);

    for (i = 0; i < argc; i++) {
        bh(atoi(argv[i]), cx, cy, flags);
    } /* for */
    if (!(flags & FL_TRACE)) {
        puts("");
        fflush(stdout);
    } /* if */
} /* main */

it draws amazing circles like this:

$ bresenham 5 10
                           * * * * * * *
                       * *               * *
                     *                       *
                   *                           *
$ _              *                               *
               *             * * * * *             *
               *           *           *           *
             *           *               *           *
             *         *                   *         *
             *         *                   *         *
             *         *                   *         *
             *         *                   *         *
             *         *                   *         *
             *           *               *           *
               *           *           *           *
               *             * * * * *             *
                 *                               *
                   *                           *
                     *                       *
                       * *               * *
                           * * * * * * *

Answer 2

Your two for loop should start from 0:

for (x = 0; x <= num * 2; x++)
{
    for (y = 0; y <= num * 2; y++)
    {
        dist = sqrt((x - num) * (x - num) + (y - num) * (y - num));
        {
            if (dist==num)
            {
                printf("O");
            }
            else
            {
                printf(" ");
            }
        }

    }
    printf("\n");

}

You are probably missing the first column and the first row.