animation of vertical bars using processing - animation

Question

I am basically trying to make a animation of vertical bars across the screen which should be equally spaced and continue until some key is pressed etc.. in the processing.org tool for animation.
I was able to get a kind of animation, but with hard coded values and had to write the same code again and again to generate the animation of bars for the whole frame/screen. I need to make it generic, so that changing the screen width or the size of the bars would not make me change the whole code but just the variables which control the parameters. Below is my code. I have written the code for three vertical bars but that needs to be done for the whole screen..
int a;
int i;
int j;
void setup() {
size(640, 360);
a = width/2;
i = 0;
}
void draw() {
background(51);
//need to avoid these repetitions each time for each bar
rect(a , 0, 25, width);
a = a - 1;
if (a < 0) {
a = width;
}
rect(i= a+50, 0, 25, width);
i = i - 1;
if (i < 0) {
i = width + a;
}
rect(j = i + 50, 0, 25, width);
j = j - 1;
if (a < 0) {
j = width + i;
}
}

Answer 1

It sounds like you're looking for an array.
An array is like a variable, only it can hold multiple values in its indexes. You can then use a for loop to iterate over the array and do stuff based on the values in the array.
Here's an example that uses an array to keep track of the line positions:
float[] linePositions = new float[10];
float lineWidth = 25;
float lineSpacing = 25;
float lineSpeed = 1;
void setup() {
size(640, 360);
for (int i = 0; i < linePositions.length; i++) {
linePositions[i] = width/2 + (lineWidth+lineSpacing)*i;
}
}
void draw() {
background(51);
//loop through the lines
for (int i = 0; i < linePositions.length; i++) {
//draw the line
rect(linePositions[i], 0, lineWidth, width);
//move the line
linePositions[i] -= lineSpeed;
//wrap the line
if ( linePositions[i] < 0) {
linePositions[i] = width;
}
}
}
More info on arrays can be found in the Processing reference.