Code
//在一个picture控件中画同心圆
Graphics graphics = pictureBox2.CreateGraphics();
Pen pen = new Pen(Brushes.Red);
//初始半径
float r0 = 10;
//圆心
float x0 = 100;
float y0 = 100;
//圆的宽度和高度
float width = 0;
float height = 0;
float x = 0;
float y = 0;
//圆半径的递增数量
float d = 20;
for (int i = 0; i < 10; i++)
{
//计算当前圆的宽度和高度
width = x0 + r0 + d*i;
height = y0 + r0 + d*i;
//计算当前圆的左上角顶点坐标
x = x0 - width / 2;
y = y0 - height / 2;
//画圆
graphics.DrawEllipse(pen, x, y, width, height);
}