一直显示 error C2065: “knots” : undeclared identifier 这个错误，本人也知道是knots未定义，但是怎么定义啊
求个高手解答，要详细一些怎么改能解决

#include <windows.h>  
#include <GL/glut.h>  
  
GLUnurbsObj *theNurb;  
GLfloat ctrlpoints[9][3] = {{0,-0.2,0},{-1.2,-0.5,0},{-1.6,-1,0},{-1.4,-1.5,0},  
{-1,-2.2,0},{-0.5,-2.7,0},{-0.35,-3.2,0},{-0.6,-3.7,0},{-1.6,-4.2,0}};//控制点  
GLfloat color[9][3]={{1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{-1.0,1.0,0.0},  
{-1.0,0.0,0.0},{-1.0,-1.0,0.0},{0.0,-1.0,0.0},{1.0,-1.0,0.0},{1.0,-1.0,0.0}};  
  
void myInit(void)  
{  
    glClearColor(1.0,1.0,1.0,0.0);//设置背景色  
    theNurb = gluNewNurbsRenderer();//创建NURBS对象theNurb  
    gluNurbsProperty(theNurb,GLU_SAMPLING_TOLERANCE,10);  
}  
/*绘制曲线*/  
void myDisplay(void)  
{  
    int i;
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);  
    glColor3f(0.0,0.0,0.0);  
    glLineWidth(3.0);  
    /*绘制曲线*/  
    gluBeginCurve(theNurb);  
    gluNurbsCurve(theNurb,13,knots,3,&ctrlpoints[0][0],4,GL_MAP1_VERTEX_3);  
    gluNurbsCurve(theNurb,13,knots,3,&color[0][0],4,GL_MAP1_COLOR_4);  
    gluEndCurve(theNurb);  
    /*绘制点*/  
    glColor3f(1.0,0.0,0.0);  
    glPointSize(5.0);  
    glBegin(GL_POINTS);  
    for(i = 0;i < 9;i++)  
        glVertex2fv(&ctrlpoints[i][0]);  
    glEnd();  
    glutSwapBuffers();  
}  
void myReshape(GLsizei w,GLsizei h)  
{  
    glViewport(0,0,w,h);  
    glMatrixMode(GL_PROJECTION);  
    glLoadIdentity();  
    if(w <=h)  
        glOrtho(-10.0,10.0,-10.0*(GLfloat)h/(GLfloat)w,10.0*(GLfloat)h/  
  
(GLfloat)w,-10.0,10.0);  
    else  
        glOrtho(-10.0*(GLfloat)w/(GLfloat)h,10.0*(GLfloat)w/(GLfloat)h,-  
  
10.0,10.0,-10.0,10.0);  
    glMatrixMode(GL_MODELVIEW);  
    glLoadIdentity();  
    glTranslatef(0.0,0.0,-9.0);  
}  
int main(int argc,char ** argv)  
{  
    glutInit(&argc,argv);  
    glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);  
    glutInitWindowSize(600,400);  
    glutInitWindowPosition(200,200);  
    glutCreateWindow("NURBS curve");  
    /*绘制与显示*/  
    myInit();  
    glutReshapeFunc(myReshape);  
    glutDisplayFunc(myDisplay);  
    glutMainLoop();  
    return(0);  
}