Converting JS to C# got some errors.

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1

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2

I made the changes to get it to compile. You did a pretty good job of the translation. Your main issue was the format of GetComponent.

using UnityEngine;
using System.Collections;
using System;
 
public class ParticleProjectionCirle : MonoBehaviour {
    public bool emit = true;
    public float range = 1.0f;
    public int particleCount = 16;
    public float particleSize = 1.0f;
    public float rotationSpeed = 0.5f;
    public Color particleColor = Color.white;
    public LayerMask layerMask = -1;
    public float castMaxDistance = Mathf.Infinity;
 
    private int oldParticleCount;
    private ParticleEmitter emitter;
    private Particle[] particles;
 
    private float rot;
 
    private Vector3 center;
    private Vector3 pos;
    private RaycastHit hit;
 
    private Transform myTransform;
 
    void Awake() {
       emitter = gameObject.GetComponent<ParticleEmitter>();
 
       if (!emitter) {
         gameObject.AddComponent("EllipsoidParticleEmitter");
         emitter = gameObject.GetComponent<ParticleEmitter>();
       }
 
       emitter.emit = false;
       emitter.ClearParticles();
       emitter.useWorldSpace = true;
 
       createParticlesAry();
 
       myTransform = transform;
    }
 
    private void createParticlesAry() {
       if (particleCount < 0) {
         particleCount = 0;
       }
 
       particles = new Particle[oldParticleCount];
       oldParticleCount = oldParticleCount;
    }
 
    private void setParticlesCount() {
       if (particles == null || (oldParticleCount != particleCount)) {
         createParticlesAry();
       }
    }
 
    void Update() {
       setParticlesCount();
       emitter.ClearParticles();
 
       if (emit) {
         float radian;
         float offsetY;
 
         center = myTransform.position;
         rot += Time.deltaTime * rotationSpeed;
         offsetY = particleSize / 2;
 
         for (int cnt = 0; cnt < particleCount; cnt++) {
          radian = (float)(Mathf.PI * (cnt / particleCount * 0.5) + rot);
          pos.x = range * Mathf.Cos(radian) + center.x;
          pos.y = center.y;
          pos.z = range * Mathf.Sin(radian) + center.z;
 
          if (Physics.Raycast(pos, -myTransform.up, out hit, castMaxDistance, layerMask)) {
              pos.y = hit.point.y + offsetY;
          }
 
          particles[cnt].position = pos;
          particles[cnt].color = particleColor;
          particles[cnt].size = particleSize;
          particles[cnt].energy = 1.0f;
          particles[cnt].velocity = myTransform.up;
         }
 
         emitter.particles = particles;
       }
    }
}