drawing canvas on html

//Creates a canvas and draws a circle
var canvas = document.body.appendChild(document.createElement("canvas"));
var ctx = canvas.getContext("2d");

ctx.beginPath();
ctx.arc(canvas.width / 2, canvas.height / 2, 50, 0, Math.PI * 2);
ctx.fillStyle = "red";
ctx.strokeStyle = "black";
ctx.stroke();
ctx.fill();

 var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");

 ctx.moveTo(0, 0);
ctx.lineTo(200, 100);

 ctx.stroke(); 

#this code creates a circle within a canvas that must be created in HTML
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95, 50, 40, 0, 2 * Math.PI);
ctx.stroke();

<canvas id="myCanvas" width="200" height="100"
style="border:1px solid 
#000000;">

</canvas>