{"id":6595,"date":"2024-10-05T00:01:15","date_gmt":"2024-10-05T07:01:15","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=6595"},"modified":"2024-10-12T09:32:48","modified_gmt":"2024-10-12T16:32:48","slug":"bouncing-an-asterisk","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=6595","title":{"rendered":"Bouncing an Asterisk"},"content":{"rendered":"

For last week’s Lesson<\/a>, I gathered various techniques to show how the terminal screen can be manipulated directly in C without using a library like Ncurses. I have a few more tricks to show.
\n
\nThe next item I’d like to pull from old code is the kbhit()<\/em> function, once popular in C programming for older (non-multitasking) operating systems. I wrote about emulating this function in another post<\/a>. As with various terminal manipulation magic, recreating the kbhit()<\/em> function involves a call to the ioctl()<\/em> function to peek into the terminal’s guts. You can read the details in the original post.<\/p>\n

My purpose for adding the kbhit()<\/em> function is to recreate the old bouncing asterisk program, which was popular with budding programmers way back when. The effect is seen as a character that traverses the screen, changing directions when it bumps into the screen’s edge.<\/p>\n

The kbhit()<\/em> function is necessary to poll the keyboard to check for a press of the Enter key, which terminates the program. I also updated the code presented in last week’s Lesson, modifying the locate()<\/em> function to not only move the cursor but to place a character at the given position. The new function is called putat()<\/em>, and it’s shown in this update to the source code file:<\/p>\n

2024_10_05-Lesson.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <time.h>\r\n#include <unistd.h>\r\n#include <sys\/ioctl.h>\r\n\r\n#define home() printf(\"\\e[H\")\r\n#define clear() printf(\"\\e[H\\e[2J\")\r\n\r\n\/* check for a key waiting *\/<\/span>\r\nint kbhit(void)\r\n{\r\n    int k;\r\n\r\n    ioctl(STDIN_FILENO,FIONREAD,&k);\r\n\r\n    return(k);\r\n}\r\n\r\n\/* set the cursor to position x (columns)\r\n   and y (rows ) and set character c *\/<\/span>\r\nvoid putat(x,y,c)\r\n{\r\n    printf(\"\\e[%d;%dH%c\",y,x,c);\r\n}\r\n\r\n\/* pause for m milliseconds *\/<\/span>\r\nvoid delay(int m)\r\n{\r\n    long pause;\r\n    clock_t now,then;\r\n\r\n    pause = m*(CLOCKS_PER_SEC\/1000);\r\n    now = then = clock();\r\n    while( (now-then) < pause )\r\n        now = clock();\r\n}\r\n\r\n\/* set an asterisk in the center of the screen *\/<\/span>\r\nint main()\r\n{\r\n    int rows,columns,posx,posy,vert,horz;\r\n    struct winsize w;\r\n    char buffer[BUFSIZ];\r\n\r\n    \/* obtain the window size *\/<\/span>\r\n    ioctl(STDOUT_FILENO, TIOCGWINSZ, &w);\r\n    rows = w.ws_row;\r\n    columns = w.ws_col;\r\n\r\n    \/* remove line buffering *\/<\/span>\r\n    setvbuf(stdout,buffer,_IONBF,BUFSIZ);\r\n\r\n    \/* initialize *\/<\/span>\r\n    clear();\r\n    puts(\"Press Enter to end\");\r\n    posx=columns\/2;\r\n    posy=rows\/2;\r\n    vert=1;\r\n    horz=1;\r\n\r\n    \/* bounce the asterisk *\/<\/span>\r\n    while(1)\r\n    {\r\n        \/* end the loop on key press *\/<\/span>\r\n        if( kbhit() )\r\n        {\r\n            getchar();\r\n            break;\r\n        }\r\n        \/* position the cursor *\/<\/span>\r\n        putat(posx,posy,'*');\r\n        delay(125);                \/* 1\/8 sec. delay *\/<\/span>\r\n        putat(posx,posy,' ');    \/* erase *\/<\/span>\r\n        \/* check bounds *\/<\/span>\r\n        if( posx==columns-1 || posx==1 )\r\n            horz=-horz;            \/* switch directions *\/<\/span>\r\n        posx += horz;\r\n        if( posy==rows-1 || posy==2 )\r\n            vert=-vert;            \/* switch directions *\/<\/span>\r\n        posy += vert;\r\n    }\r\n    \/* set the cursor and say goodbye *\/<\/span>\r\n    putat(1,rows-1,'B');\r\n    puts(\"ye!\");\r\n\r\n    return 0;\r\n}<\/pre>\n
This code adds four new int<\/em> variables to track the bouncing asterisk: posx<\/code>, posy<\/code>, vert<\/code>, and horz<\/code>. The posx<\/code> and posy<\/code> variables contain the asterisk’s column and row positions. The vert<\/code> and horz<\/code> variables hold 1 or -1 to set the direction.<\/p>\n
The bouncing action takes place in the endless while<\/em> loop. The kbhit()<\/em> function terminates the loop when the user presses the Enter key. (It’s not a perfect substitute for the original kbhit()<\/em> as other characters entered appear in the output.)<\/p>\n
Within the loop, the asterisk is positioned, execution delays for 125 milliseconds, then the asterisk is erased. An if<\/em> test checks for the edges of the terminal window. When encountered, the horz<\/code> or vert<\/code> variables are inverted, changing the asterisk’s direction. This action repeats until the user presses Enter.<\/p>\n
Figure 1 shows a sample run.<\/p>\n
\"\"
Figure 1. The program’s sample run.<\/p><\/div>\n
I continue messing with these features in next week’s Lesson<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
How to manipulate the screen and the keyboard without using a library like Ncurses. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-6595","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6595","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6595"}],"version-history":[{"count":5,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6595\/revisions"}],"predecessor-version":[{"id":6628,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/6595\/revisions\/6628"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6595"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6595"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6595"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}