C# To write in a text file

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C#

Hello !

I want to write every data at each frame :

    void FixedUpdate() {

        // To associate names_markers to avatar_joints :
        if (frame < nv_data [0].positions.Length) {

            for (int k = 0; k < body.Length; ++k) {

                                if (body [k] != null) { 

           body[k].transform.localPosition = nv_data[k].positions [frame] / 1000;
                                } else
                                        continue;
                        }

            if (frame < forces_dup.Length) {

                if (frame > 1) {

StreamWriter writer = new StreamWriter ("1_forces_reelles_virtuelles.txt");

                        using (writer) {

writer.WriteLine ((40 * nv_data [55].positions [frame] - nv_data [55].positions [frame - 1]).magnitude / (1000 * Time.deltaTime));
writer.WriteLine (forces_dup [frame].magnitude / 1000);

                    }
                }
            }

        frame++;

    }

}

And in the text file, it appears only the last datas of :
- (40 * nv_data [55].positions [frame] - nv_data [55].positions [frame - 1]).magnitude / (1000 * Time.deltaTime)
- forces_dup [frame].magnitude / 1000

When I use "Debug.Log" to show datas, all appear in the console.
I assume that the other lines are erased at each frame.

How can I save every line of datas ?

I try to do it in void Update (but it's the same result) :

// Update is called once per frame
void Update() {

    string forces_virtuelles;
    string forces_reelles;

    if (frame < forces_dup.Length) {

        if (frame > 1) {

            forces_virtuelles = ((40 * nv_data [55].positions [frame] - nv_data [55].positions [frame - 1]).magnitude / (1000 * Time.deltaTime)).ToString();
            forces_reelles = (forces_dup[frame].magnitude/1000).ToString();

StreamWriter writer = new StreamWriter ("1_forces_reelles_virtuelles.txt");

            using (writer) {

                writer.WriteLine (forces_virtuelles + "\n");
                writer.WriteLine (forces_reelles + "\n");

            }

        }

    }

}

The first part runs well, even with the second part :

    void FixedUpdate() {

        // To associate names_markers to avatar_joints :
        if (frame < nv_data [0].positions.Length) {

            for (int k = 0; k < body.Length; ++k) {

                                if (body [k] != null) { 

           body[k].transform.localPosition = nv_data[k].positions [frame] / 1000;
                                } else
                                        continue;
                        }

            }

        frame++;

    }

}

Can you help me please ?