Calculating walkingdirection

Stupid question.

Im thought about making a simple game seen from above where you move a character around.
I thought that when pressing a button the character walks forward, and with left / right key he turns.
Alternaly walk forward with a button, set direction with the mouse.

So my question is, how to achive this, it seems very simple, but i cant figure it out.

Thanks.

x = x+ (cos(walk_angle)*walk_distance)
y = y+ (sin(walk_angle) *walk_distance)