i changed

xpos += (float)sin(heading*piover180) * 0.05f;
zpos += (float)cos(heading*piover180) * 0.05f;
into

xpos += (float)sin(heading*piover180) * 0.0005f;
zpos += (float)cos(heading*piover180) * 0.0005f;
then i run the program finding the scene shakes when i press UP or DOWN to move,
it doesn't move in a smooth way, can anyone tell how to solve this?

It's most likely because the lesson doesn't use a delta time value, instead movement is based on how many frames are rendered, so any inconsistencies in the frame rate show up as shaking or stuttering in the movements, adding delta time compensates for that, so do skip ahead to lesson 32 an learn how to implement it.

thank you