C++ Programming Code Examples
C++ > Computer Graphics Code Examples
Animated Circles In C++
/* Animated Circles In C++ */
#include<stdlib.h>
#include<conio.h>
#include<graphics.h>
#include<dos.h>
void main()
{
int x,y,i;
int g=DETECT,d;
initgraph(&g,&d,"\tc\bgi");
cleardevice();
x=getmaxx()/2;
y=getmaxy()/2;
settextstyle(TRIPLEX_FONT, HORIZ_DIR, 3);
setbkcolor(rand());
setcolor(4);
outtextxy(30,100,"Press");
outtextxy(30,130,"any");
outtextxy(30,160,"key");
outtextxy(30,190, "to");
outtextxy(30,220,"Quit");
while (!kbhit())
{
setcolor(rand());
for (int i=0;i<50;i++)
circle(x,y,i );
setcolor(rand());
for (int j=70;j<120;j++)
circle(x,y,j);
setcolor(rand());
for (int k=140;k<190;k++)
circle(x,y,k);
setcolor(rand());
for (int l=210;l<230;l++)
circle(x,y,l);
delay(200);
}
getch();
closegraph();
}
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
The header file graphics.h contains getmaxy() function which returns the maximum Y coordinate for current graphics mode and driver. getmaxy returns the maximum (screen-relative) y value for the current graphics driver and mode. For example, on a CGA in 320*200 mode, getmaxy returns 199. getmaxy is invaluable for centering, determining the boundaries of a region onscreen, and so on.
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
The getch() is a predefined non-standard function that is defined in conio.h header file. It is mostly used by the Dev C/C++, MS- DOS's compilers like Turbo C to hold the screen until the user passes a single value to exit from the console screen. It can also be used to read a single byte character or string from the keyboard and then print. It does not hold any parameters. It has no buffer area to store the input character in a program. The getch() function does not accept any parameter from the user. It returns the ASCII value of the key pressed by the user as an input.
Settextstyle function is used to change the way in which text appears, using it we can modify the size of text, change direction of text and change the font of text. settextstyle sets the text font, the direction in which text is displayed, and the size of the characters. A call to settextstyle affects all text output by outtext and outtextxy.
setcolor() function is used to set the foreground color in graphics mode. After resetting the foreground color you will get the text or any other shape which you want to draw in that color. setcolor sets the current drawing color to color, which can range from 0 to getmaxcolor. The current drawing color is the value to which pixels are set when lines, and so on are drawn. The drawing colors shown below are available for the CGA and EGA, respectively.
Generate random number. Returns a pseudo-random integral number in the range between 0 and RAND_MAX. This number is generated by an algorithm that returns a sequence of apparently non-related numbers each time it is called. This algorithm uses a seed to generate the series, which should be initialized to some distinctive value using function srand. RAND_MAX is a constant defined in <cstdlib>. The rand() function in C++ is used to generate random numbers; it will generate the same number every time we run the program. In order to seed the rand() function, srand(unsigned int seed) is used. The srand() function sets the initial point for generating the pseudo-random numbers. The rand() function generates numbers randomly.
To create a program in Graphics Mode, the first step would be to include the header file graphics.h. This file is required for Graphics programming. After this, the graphics have to be initialized. C Language supports 16 Bit's MS-DOS environment. Initializing the Graphics mode is to call various functions, one such is called initgraph. initgraph initializes the graphics system by loading a graphics driver from disk (or validating a registered driver), and putting the system into graphics mode. To start the graphics system, first call the initgraph function. initgraph loads the graphics driver and puts the system into graphics mode. You can tell initgraph to use a particular graphics driver and mode, or to autodetect the attached video adapter at run time and pick the corresponding driver. If you tell initgraph to autodetect, it calls detectgraph to select a graphics driver and mode. initgraph also resets all graphics settings to their defaults (current position, palette, color, viewport, and so on)
delay() function is used to hold the program's execution for given number of milliseconds, it is declared in dos.h header file. There can be many instances when we need to create a delay in our programs. C++ provides us with an easy way to do so. We can use a delay() function for this purpose in our code. We can run the code after a specific time in C++ using delay() function.
The header file graphics.h contains closegraph() function which closes the graphics mode, deallocates all memory allocated by graphics system and restores the screen to the mode it was in before you called initgraph. closegraph() function is used to re-enter in the text mode and exit from the graphics mode. If you want to use both text mode and graphics mode in the program then you have to use both initgraph() and closegraph() function in the program. This function deallocates all memory allocated by graphics system and restores the screen to that mode in which it was presented before you called the initgraph() function.
outtextxy displays a text string in the viewport at the given position (x, y), using the current justification settings and the current font, direction, and size. To maintain code compatibility when using several fonts, use textwidth and textheight to determine the dimensions of the string. If a string is printed with the default font using outtext or outtextxy, any part of the string that extends outside the current viewport is truncated. outtextxy is for use in graphics mode; it will not work in text mode.
The header file graphics.h contains getmaxx() function which returns the maximum X coordinate for current graphics mode and driver. getmaxx() returns the maximum (screen-relative) x value for the current graphics driver and mode. For example, on a CGA in 320*200 mode, getmaxx returns 319. getmaxx is invaluable for centering, determining the boundaries of a region onscreen, and so on.
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
The kbhit is basically the Keyboard Hit. This function is present at conio.h header file. So for using this, we have to include this header file into our code. The functionality of kbhit() is that, when a key is pressed it returns nonzero value, otherwise returns zero. kbhit() is used to determine if a key has been pressed or not. If a key has been pressed then it returns a non zero value otherwise returns zero.
This library function is declared in graphics.h and used to draw a circle; it takes centre point coordinates and radius. Circle function is used to draw a circle with center (x,y) and third parameter specifies the radius of the circle. The code given below draws a circle. Where, (x, y) is center of the circle. 'radius' is the Radius of the circle.
The header file graphics.h contains cleardevice() function. cleardevice() is a function which is used to clear the screen by filling the whole screen with the current background color. It means that cleardevice() function is used to clear the whole screen with the current background color and it also sets the current position to (0,0). Both clrscr() and cleardevice() functions are used to clear the screen but clrscr() is used in text mode and cleardevice function is used in the graphics mode.
setbkcolor() function is used to set the background color in graphics mode. The default background color is black and default drawing color as we know is white. setbkcolor() function takes only one argument it would be either the name of color defined in graphics.h header file or number associated with those colors. If we write setbkcolor(yellow) it changes the background color in Green. The possible color values are from 0 - 15 black, blue, green, cyan, red, magenta, brown, lightgray, darkgray, lightblue, lightgreen, lightcyan, lightred, lightmagenta, yellow, white and blink (128).
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