Variable Scope

/**
 * Variable Scope. 
 * 
 * Variables have a global or local "scope". 
 * For example, variables declared within either the
 * setup() or draw() functions may be only used in these
 * functions. Global variables, variables declared outside
 * of setup() and draw(), may be used anywhere within the program.
 * If a local variable is declared with the same name as a
 * global variable, the program will use the local variable to make 
 * its calculations within the current scope. Variables are localized
 * within each block, the space between a { and }. 
 */
 
int a = 80;  // Create a global variable "a"

void setup() {
    size(640, 360);
    background(0);
    stroke(255);
    noLoop();
}

void draw() {
    // Draw a line using the global variable "a"
    line(a, 0, a, height);
  
    // Create a new variable "a" local to the for() statement 
    for (int a = 120; a < 200; a += 2) {
        line(a, 0, a, height);
    }
  
    // Create a new variable "a" local to the draw() function
    int a = 300;

    // Draw a line using the new local variable "a"
    line(a, 0, a, height);  
  
    // Make a call to the custom function drawAnotherLine()
    drawAnotherLine();
  
    // Make a call to the custom function setYetAnotherLine()
    drawYetAnotherLine();
}

void drawAnotherLine() {
    // Create a new variable "a" local to this method
    int a = 320;

    // Draw a line using the local variable "a"
    line(a, 0, a, height);
}

void drawYetAnotherLine() {
    // Because no new local variable "a" is set, 
    // this line draws using the original global
    // variable "a", which is set to the value 80.
    line(a + 2, 0, a + 2, height);
}