can any one explain boundry fill c program recursive function call's ?

faizaan · 2009-08-13T20:10:12+00:00

hi friend's, i want to know about how the recursive call are made in program given below .(the program is running properly ) #include<stdio.h> #include<conio.h> #include<graphics.h> void fillcolor(int,int,int,int); void main() { int gdriver=DETECT,gmode; int xc,yc,r,fc,bc; clrscr(); initgraph(&gdriver,&gmode,"f:\\tc\\bgi"); printf("enter center & radius : "); scanf("%d %d %d",&xc,&yc,&r); printf("enter boundry & fill color : "); scanf("%d %d",&bc,&fc); setcolor(bc); circle(xc,yc,r); fillcolor(xc,yc,bc,fc); getch(); } void fillcolor(int x,int y,int bc,int fc) { int cp; cp=getpixel(x,y); if(cp!=bc && cp!=fc) { delay(20); putpixel(x,y,fc); fillcolor(x+1,y,bc,fc); fillcolor(x-1,y,bc,fc); fillcolor(x,y+1,bc,fc); fillcolor(x,y-1,bc,fc); } } my problem is that i think that when the function is called first time then the recursive call fillcolor(x+1,y,bc,fc) will proceed in x direction and when boundry is reaches than the if(cp!=bc && cp!=fc) condition will be false and the control should return to main . But it is not happening like this so can any one explain this recursive calls to me . pls reply soon .

can any one explain boundry fill c program recursive function call's ?

faizaan

Member

Updated: Oct 27, 2024

Views: 1.1K

hi friend's,

i want to know about how the recursive call are made in program given below .(the program is running properly )

#include<stdio.h>
#include<conio.h>
#include<graphics.h>
void fillcolor(int,int,int,int);
void main()
{
int gdriver=DETECT,gmode;
int xc,yc,r,fc,bc;
clrscr();
initgraph(&gdriver,&gmode,"f:\\tc\\bgi");
printf("enter center & radius : ");
scanf("%d %d %d",&xc,&yc,&r);
printf("enter boundry & fill color : ");
scanf("%d %d",&bc,&fc);
setcolor(bc);
circle(xc,yc,r);
fillcolor(xc,yc,bc,fc);
getch();
}

void fillcolor(int x,int y,int bc,int fc)
{
int cp;
cp=getpixel(x,y);

if(cp!=bc && cp!=fc)
{
delay(20);
putpixel(x,y,fc);
fillcolor(x+1,y,bc,fc);
fillcolor(x-1,y,bc,fc);
fillcolor(x,y+1,bc,fc);
fillcolor(x,y-1,bc,fc);
}
}

my problem is that i think that when the function is called first time
then the recursive call fillcolor(x+1,y,bc,fc) will proceed in x direction and when boundry is reaches than the if(cp!=bc && cp!=fc) condition will be false and the control should return to main .

But it is not happening like this so can any one explain this recursive calls to me .

pls reply soon .

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mech_guy

Member • Aug 14, 2009

Hi faizaan,

my problem is that i think that when the function is called first time
then the recursive call fillcolor(x+1,y,bc,fc) will proceed in x direction and when boundry is reaches than the if(cp!=bc && cp!=fc) condition will be false and the control should return to main .
No the control wont transfer back to main after fillcolor(x+1,y,bc,fc) reaches boundary.

1. Initially you are passing Centre of circle (xc, yc) to fillcolor from main.
2. Fillcolour will fill this (xc, yc) corresponding pixel and will call itself sending it (x+1) and y coordinate.
3. This process of increasing x by 1 goes on till fillcolour catches boundary that is (xc + radius,y).
4. Once the condition gets FALSE, control gets back to "fillcolor" with coordinares (xc + radius -1,y).
5. For coordinate (xc + radius -1,y). condition says FALSE again because that pixel is already colored.
6. Control gets back to fillcolor again with coordinates (xc + radius - 2,y). Which is FALSE again.
7. This condition goes on till fillcolor reaches back to centre (xc,yc).

NOTE: Till now fillcolor(x+1,y,bc,fc) line alone was executed. to colour all pixels till right boundary. It was moved back to origin due to second line fillcolor(x-1,y,bc,fc).

Now Next line of fillcolor gets executed: fillcolor(x-1,y,bc,fc), leading to coloring of left (to centre) pixels and first line fillcolor(x+1,y,bc,fc) brings it back to origin.

8. Now same thing goes till u reach left boundary of circle. And then control starts shifting back to origin again.
9. Now 3rd line of fillcolor(x,y+1,bc,fc) gets executed. Come back to origin and finally start colouring (y-1) pixels.
10. Come back to origin.
11. Now none of the commands of fillcolour is left to be exceuted.
12. It is now that command goes back to main.

Hope its clear now.

Thanks

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faizaan

Member • Aug 14, 2009

thank's mech_guy,

great explaination keep it up.

But

"Control gets back to fillcolor again with coordinates (xc + radius - 2,y). Which is FALSE again."

i think that after reaching boundry it will go to fillcolor(x,y+1,bc,fc) because fillcolor(x-1,y,bc,fc) is again false.

i tried introducing delay(100) in between function call's and i studied the pattern in which it was filling .

but when i introduced delay between

fillcolor(x,y+1,bc,fc);
delay(100);
fillcolor(x,y-1,bc,fc);

the result is amazing it is not as simple as we think.

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dipen30

Member • Aug 14, 2009

you are right faizaan for

fillcolor(x,y+1,bc,fc);
delay(100);
fillcolor(x,y-1,bc,fc);

this functions..

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