Conditions are like questions. They allow a program to decide to take one action if the answer to a question is true or to do another action if the answer to the question is false. The questions asked within a program are always logical or relational statements. For example, if the variable 'i' is equal to zero then draw a line.
Original Processing.org Example: Conditionals1
// All Examples Written by Casey Reas and Ben Fry
// unless otherwise stated.
size(200, 200);
background(0);
for(int i=10; i<width; i+=10) {
// If 'i' divides by 20 with no remainder draw the first line
// else draw the second line
if(i%20 == 0) {
stroke(153);
line(i, 40, i, height/2);
} else {
stroke(102);
line(i, 20, i, 180);
}
}