.net drawlines with pens(different colors) in a loop

Question

I want to draw lines ( about 100 ) with different colors. The lines will draw in a loop and get random colors. Here is my code:

for( int i = 0; i < 100 < i++ )
{
srand( time(NULL) );
int index = rand() % 99;
Pen^  my_pen = gcnew Pen((Color)CustomColorTables[index]);
g->drawLine(my_pen,startPointAray[i],stopPointArray[i]);
}

But it draws all lines with the same color???

Note: I checked the random values, there is no problem about generating random values.

score 1 · Accepted Answer · answered Dec 09 '11 at 13:33

1

Try to place the line:

srand( time(NULL) );

BEFORE entering the for loop. In your case you are resetting each time the pseudo random sequence and you probably obtain a wrong sequence. Then use:

int index = (100*rand()) % 99;

because rand() by itself returns a number from 0 to 1 and you will always receive 99 as a % result.

answered Dec 09 '11 at 13:33

Felice Pollano

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@user983924 even by multiplying rand()*100 before ? – Felice Pollano Dec 09 '11 at 13:39
I replaced the srand function before the loop and the problem is solved. Thanks – user983924 Dec 09 '11 at 14:04
No, `rand()` returns an integer in the range 0 to `RAND_MAX`. And even if it did return a number from 0 to 1, you wouldn't get 99 from the modulo operation. – Ben Voigt Dec 10 '11 at 18:45

score 0 · Answer 2 · answered Dec 09 '11 at 13:31

0

try to replace:

CustomColorTables[index];

with:

CustomColorTables[i];

if it works better than before as I believe, the issue is in the way you generate and use the random value index.

answered Dec 09 '11 at 13:31

Davide Piras

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It draws the same, I think the problem is about the pen. – user983924 Dec 09 '11 at 13:35
how many colors and with which value do you have in the CustomColorTables variable? – Davide Piras Dec 09 '11 at 13:37
100 colors and I cretaed the color table. – user983924 Dec 09 '11 at 13:39

.net drawlines with pens(different colors) in a loop

2 Answers2