Unity3D Graphing Calculator

using UnityEngine;
using System.Collections;

public class Graph : MonoBehaviour {

    Vector3 zero = new Vector3(0, 0, 0);
    Vector3 zero2 = new Vector3(0, 0, 0);
    //Line 1
    string slp;
    string ynt;
    //Line 2
    string slp2;
    string ynt2;


    string currentMenu = "GUI";
    public GameObject line1;
    public GameObject line2;

    void Start() {
        slp = "";
        ynt = "";

        slp2 = "";
        ynt2 = "";
    }

    void OnGUI() {
        if(currentMenu == "GUI")
            GraphUI();
    }

    void GraphUI() {

        GUI.Box(new Rect(0, 0, 300, Screen.height), "Graphing Calculator");
        //Line 1
        GUI.Label(new Rect(10, 30, 100, 20), "Y-Intercept 1");
        ynt = GUI.TextField(new Rect(10, 50, 280, 60), ynt);
        GUI.Label(new Rect(10, 120, 100, 20), "Slope 1");
        slp = GUI.TextField(new Rect(10, 140, 280, 60), slp);
        //Line 2

        GUI.Label(new Rect(10, 240, 100, 20), "Y-Intercept 2");
        ynt2 = GUI.TextField(new Rect(10, 260, 280, 60), ynt2);
        GUI.Label(new Rect(10, 330, 100, 20), "Slope 2");
        slp2 = GUI.TextField(new Rect(10, 350, 280, 60), slp2);

        if(GUI.Button(new Rect(10, 420, 280, 60), "Calculate and Graph")) {
            if((slp != null && slp != "") && (ynt != null && ynt != "")) {
                Calculate(slp, ynt, slp2, ynt2);
            } else {
                Debug.LogWarning("Parameters Not Complete");
            }
        }

        if(GUI.Button(new Rect(10, Screen.height - 70, 280, 60), "Reset Graph")) {
            slp = "";
            ynt = "";
            slp2 = "";
            ynt2 = "";

            GameObject[] points = GameObject.FindGameObjectsWithTag("GraphPoint");
            foreach (GameObject target in points) {
                GameObject.Destroy(target);
            }
        }
    }

    //Line 1
    void Calculate(string sl, string yt, string sl2, string yt2) {
        int nextNumber = 1;
        StartCoroutine(Calculate2(sl2, yt2));
        float slope = float.Parse(sl);
        float yint = float.Parse(yt);
        float y = yint;
        float x = slope;
        zero.y = y;
        zero.x = 0;

        for(int i = 0;i < 5;i++) {
            Object redPoint = Instantiate(line1, zero, Quaternion.identity);
            redPoint.name = "Red" + nextNumber;
            nextNumber++;
            zero.y = zero.y + slope;
            zero.x = zero.x += 1;
        }

        zero.y = 0;
        zero.x = 0;
        nextNumber = 1;
        //CalculateAngle(GameObject.Find("Red1"), GameObject.Find("Red2"));
        CalculateAngle(GameObject.Find("Red1"), GameObject.Find("Red2"));
    }

    //Line 2
    IEnumerator Calculate2(string sl, string yt) {
        yield return new WaitForSeconds(0.0f);
        int nextNumber = 1;
        float slope = float.Parse(sl);
        float yint = float.Parse(yt);
        float y = yint;
        float x = slope;
        zero2.y = y;
        zero2.x = 0;

        for(int i = 0;i < 5;i++) {
            Object yellowPoint = Instantiate(line2, zero2, Quaternion.identity);
            yellowPoint.name = "Yellow" + nextNumber;
            nextNumber++;
            zero2.y = zero2.y + slope;
            zero2.x = zero2.x += 1;
        }
        zero2.y = 0;
        zero2.x = 0;
        nextNumber = 1;
    }

    void CalculateAngle(GameObject x, GameObject y) {
        float xDis = y.transform.position.x - x.transform.position.x;
        float yDis = y.transform.position.y - x.transform.position.y;

        Debug.Log(xDis + " : " + yDis);
    }
}