2D Movement for 4 directions only working left/right - unity3d

Question

I have problem I want to make my player move in 4 directions: UP,DOWN,LEFT AND RIGHT ... here is my script
using UnityEngine;
using System.Collections;
public class MovingPlayer : MonoBehaviour {
float speed = 4f;
// Update is called once per frame
void Update () {
if (Input.GetKey (KeyCode.A)) {
transform.Translate(Vector2.right * speed * Time.deltaTime);
}
else if (Input.GetKey (KeyCode.D)) {
transform.Translate(-Vector2.right * speed * Time.deltaTime);
}
else if (Input.GetKey (KeyCode.W)) {
transform.Translate(Vector2.up * speed * Time.deltaTime);
}
else if (Input.GetKey (KeyCode.S)) {
transform.Translate(-Vector2.up * speed * Time.deltaTime);
}
}
}
And it is working just for left and right , not up and down !?

Answer 1

Your code uses else if for all four directions. This means that the character can only move in one direction at a time. If 'A' is pressed, then all of the else branches are ignored. If 'D' is pressed the 'W' and 'S' branches are ignored.
It makes sense to use else if when swapping between left and right, or between up and down, since the player should only be able to move one direction on a given axis at a time. But the horizontal and vertical sections should be independent if conditions:
if (Input.GetKey (KeyCode.A)) {
transform.Translate(Vector2.right * speed * Time.deltaTime);
}
else if (Input.GetKey (KeyCode.D)) {
transform.Translate(-Vector2.right * speed * Time.deltaTime);
}
if (Input.GetKey (KeyCode.W)) {
transform.Translate(Vector2.up * speed * Time.deltaTime);
}
else if (Input.GetKey (KeyCode.S)) {
transform.Translate(-Vector2.up * speed * Time.deltaTime);
}
I would also recommend looking at the Input class in the unity documentation. The input manager allows you to define input axes (based on keyboard, mouse, or joystick input), and read them as a continuous value on the range [-1, 1]. Unity defines two default axes called "Horizontal" and "Vertical" which read input from AD and WS respectively. To use virtual axes, you can use:
transform.Translate(Vector2.right * Input.GetAxis("Horizontal") * Time.deltaTime);
transform.Translate(Vector2.up * Input.GetAxis("Vertical") * Time.deltaTime);

Answer 2

Try this, it moves the object relating to the global coordinates:
(...)
else if (Input.GetKey (KeyCode.W)) {
transform.Translate(0, Vector2.up * speed * Time.deltaTime, Space.World);
}
else if (Input.GetKey (KeyCode.S)) {
transform.Translate(0, -Vector2.up * speed * Time.deltaTime, Space.World);
}