"c_setminmax (ENTITY*)
Sets the collision ellipsiod and bounding box coordinates of the entity to it's real proportions (a bounding box around all it's frames)"

You should try c_updatehull to create a bounding box that surrounds the stand/walk frame.


BTW: You did not understand the while-loop yet, jump_percentage is not supposed to be exactly 0, but lower equal than 0 (so the condition (jump_percentage > 0) is not true). F.i. let time_step be 1 and jump_percentage = 2.3. After the loop

while(jump_percentage > 0)
jump_percentage -= 3* time_step;
wait(1);
}

jump_percentage will be -0.7. The simple solution:

while(jump_percentage > 0)
jump_percentage -= 3* time_step;
wait(1);
}
jump_percentage = 0;