float freq = 2;
float amp=-(height/4);

void setup(){
  size(1000,400);  
}

void draw(){
  background(0);
  
  //sizes
  int widthSquare = 10;
  
  stroke(122);
  
  //draw x lines
  int y=0;
  for (int i=0; i<((height)/widthSquare)+1; i++){
    line (0,y,width,y);
    y+=widthSquare;
  }
  
  //draw y lines
  int x=0;
  for (int i=0; i<(width/widthSquare); i++){
    line (x,0,x,height);
    x+=widthSquare;
  }
  
  //draw axies
  stroke(0,255,0);
  line (0,(height)/2,width,(height)/2);//x axis
  line (width/2,0,width/2,height);//y axis
  
  //draw sine wave
  stroke(0,255,0);
  float fx=(height/2)+(((height/2)+amp)*-sin((freq*TWO_PI/width)));
  for (int i=1; i<width; i++){
    line(i-1,fx,i,(height/2)+(((height/2)+amp)*-sin((freq*TWO_PI/(width))*i)));
    fx=(height/2)+(((height/2)+amp)*-sin((freq*TWO_PI/(width))*i));
  }
}

void keyPressed() {
  if (key==CODED){
    if (keyCode==UP){
      amp+=(height/40);
    }
    if (keyCode==DOWN){
      amp-=(height/40);
    }
    if (keyCode==LEFT){
      freq-=0.25;
    }
    if (keyCode==RIGHT){
      freq+=0.25;
    }
  }
}