boolean aON=false;
boolean bON=false;

void setup() {
  size(500,500);
  background(255); 
  smooth();
}

void draw() {
  if(aON) {
    drawLine1();
  }
  if(bON) {
    background(255);
  }
  if(aON = true) {
    aON = false;
  }
  if(bON = true) {
    bON = false;
  }
  if (mousePressed == true) {
    aON = true;
    } 
    else {
      aON = false;
    }
  }
  
void keyTyped() {  
  if(keyPressed) {
    if (key == '5') {
      bON = true;
    } 
    else {
      bON = false;
    }
  }
}

void drawLine1() {
  stroke(0);
  if (key == '1') {
    line(mouseX,mouseY,0,0);
  }
  if (key == '2') {
    line(mouseX,mouseY,500,0);
  }
  if (key == '3') {
    line(mouseX,mouseY,0,500);
  }
  if (key == '4') {
    line(mouseX,mouseY,500,500);
  }   
}