Operator Precedence and Associativity Rules in C

assoc-background.c

#include<stdlib.h>
#include<X11/Xlib.h>
#include<string.h>
#include<stdio.h>

#define NCOLORS 3
const char *const assoc[] = {
  "()       function call                      left-to-right",
  "[]       array element                                   ",
  ".        structure or union member                       ",
  "->       pointer reference to structure                  ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "!        logical not                        right-to-left",
  "~        bitwise complement                              ",
  "-        unary minus                                     ",
  "++       increment                                       ",
  "--       decrement                                       ",
  "&        address of                                      ",
  "*        contents of                                     ",
  "(type)   cast to type                                    ",
  "sizeof   size in bytes                                   ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "*        multiply                           left-to-right",
  "/        divide                                          ",
  "%        remainder                                       ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "+        add                                left-to-right",
  "-        subtract                                        ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "<<       bitwise left shift                 left-to-right",
  ">>       bitwise right shift                             ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "<        arithmetic less than               left-to-right",
  ">        arithmetic greater than                         ",
  "<=       arithmetic l than or equal to                   ",
  ">=       arithmetic g than or equal to                   ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "==       arithmetic equal                   left-to-right",
  "!=       arithmetic not equal                            ",
//  "─────────────────────────────────────────────────────────",
  "                                                         ",
  "&        bitwise and                        left-to-right",
  "^        bitwise exclusive or               left-to-right",
  "|        bitwise or                         left-to-right",
  "&&       logical and                        left-to-right",
  "||       logical or                         left-to-right",
  "? :      conditional expression             right-to-left",
  "=        assignment operator                right-to-left",
  ",        sequential expression              left-to-right"
};
void
load_font(Display *dpy, XFontStruct **font_info) {
  const char *fontname = "9x15";
  /* Access font */
  if ((*font_info = XLoadQueryFont(dpy, fontname)) == NULL)
  {
    (void) fprintf( stderr, "Basic: Cannot open font: %s\n", fontname);
    exit( -1 );
  }
}
void
draw_assoc(Display *dpy, Pixmap pix, GC g, XFontStruct *font_info) {
  const int x_offset = 15;
  const int y_offset = 15;
  const int font_height = font_info->ascent + font_info->descent;
  const int rowlen = strlen(assoc[1]);

  int row = row;
  for (row = sizeof(assoc) / sizeof(assoc[1]); row--;) {
    XDrawString(dpy, pix, g, x_offset, y_offset + font_height * row, assoc[row], rowlen);
  }
}
int
main () {
  Display *dpy;
  Window root;
  XWindowAttributes wa;
  GC g;
  Pixmap pix;
  const unsigned long color_green = 0x12EE12;

  /* open the display (connect to the X server) */
  dpy = XOpenDisplay (getenv ("DISPLAY"));

  /* get the root window */
  root = DefaultRootWindow (dpy);


  /* get attributes of the root window */
  XGetWindowAttributes(dpy, root, &wa);


  /* create a GC for drawing */
  g = XCreateGC (dpy, root, 0, NULL);


  /* create a pixmap as large as the root window */
  pix = XCreatePixmap (dpy, root, wa.width, wa.height, wa.depth);

  /* clear the pixmap (not done by default) */
  //  XSetForeground(dpy, g, WhitePixelOfScreen(DefaultScreenOfDisplay(dpy)) );
  //  XSetForeground(dpy, g, BlackPixelOfScreen(DefaultScreenOfDisplay(dpy)) );
  //  XFillRectangle (dpy, pix, g, 0, 0, wa.width, wa.height);

  XSetForeground(dpy, g, color_green);

  /* set the pixmap as the background of the root window */
  XSetWindowBackgroundPixmap (dpy, root, pix);

  XFontStruct *font_info;
  load_font(dpy, &font_info);
  draw_assoc(dpy, pix, g, font_info);

  /* clear the root window to make the pixmap visible */
  XClearWindow (dpy, root);

  XCloseDisplay (dpy);

  return 0;
}