trying to solve a NullReference not handled error(array trouble)

I have an error that says Object reference not set to an instance of an object
the program takes a string of DNA characters from a text file and converts them to RNA by way of a for loop and a series of if statements which do the actual conversion. the program doesnt show any syntax errors but when I try to Run the program it hangs up on the first if statement which gives me the error. I originally wrote this code In C++ and the program looks a bit different and the array is a char array instead of a string array. I was thinking that had something to do with it but when I change it back to char i have to give the array size about [500] just so it will be in bounds and this time nothing will print out in my text box. I guess what I'm asking is how do I make this array dynamic and how do I solve the problem of my results not printing when I put a large enough value of elements.

Basically what would you do different here?

here's my code

Code:

---

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


namespace bioinformaticsCal
{

    public partial class Form1 : Form
    {
        int numberOfCodons;
        int rnaLength;
        int beginIndex;
        int endIndex;
        int i;
        int j;
        int k;
        string[] codons = { "UUU", "UUC", "UUA", "UUG", "UCU", "UCC", "UCA", "UCG", "UAU", "UAC", "UAA", "UAG", "UGU", "UGC", "UGA", "UGG", "CUU", "CUC", "CUA", "CUG", "CCU", "CCC", "CCA", "CCG", "CAU", "CAC", "CAA", "CAG", "CGU", "CGC", "CGA", "CGG", "AUU", "AUC", "AUA", "AUG", "ACU", "ACC", "ACA", "ACG", "AAU", "AAC", "AAA", "AAG", "AGU", "AGC", "AGA", "AGG", "GUU", "GUC", "GUA", "GUG", "GCU", "GCC", "GCA", "GCG", "GAU", "GAC", "GAA", "GAG", "GGU", "GGC", "GGA", "GGG" };
        string[] aminoAcids = { "Phenylalanine", "Phenylalanine", "Leucine", "Leucine", "Serine", "Serine", "Serine", "Serine", "Tyrosine", "Tyrosine", "Stop", "Stop", "Cysteine", "Cysteine", "Stop", "Tryptophan", "Leucine", "Leucine", "Leucine", "Leucine", "Proline", "Proline", "Proline", "Proline", "Histidine", "Histidine", "Glutamine", "Glutamine", "Arginine", "Arginine", "Arginine", "Arginine", "Isoleucine", "Isoleucine", "Isoleucine", "Methionine", "Threonine", "Threonine", "Threonine", "Threonine", "Asparagine", "Asparagine", "Lysine", "Lysine", "Serineine", "Serineine", "Arginine", "Arginine", "Valine", "Valine", "Valine", "Valine", "Alanine", "Alanine", "Alanine", "Alanine", "Aspartate", "Aspartate", "Glutamate", "Glutamate", "Glycine", "Glycine", "Glycine", "Glycine" };
        string codon = "";
        string protein = "";
        string [] DNA;
       
        string RNA;
        string SEQ;
        int len;
     
       
        public Form1()
        {
            InitializeComponent();
        }
     
     
        private void Form1_Load(object sender, EventArgs e)
        {
            string path = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            if (!Directory.Exists(path + "\\Bioinformatics Data Files - Jason"))
                Directory.CreateDirectory(path + "\\Bioinformatics Data Files - Jason");
            if (!File.Exists(path + "\\Bioinformatics Data Files - Jason\\settings.xml"))
                File.Create((path + "\\Bioinformatics Data Files - Jason\\settings.xml"));
            File.Create((path + "\\Bioinformatics Data Files - Jason\\TextFiles.txt"));

        }



        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog Fd = new OpenFileDialog();
            if (Fd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                StreamReader Sr = new StreamReader(File.OpenRead(Fd.FileName));
                //RNA = Sr.ReadToEnd();
              SEQ = Sr.ReadToEnd();

              string strCompare = SEQ;
              string strStringContains = "T";
              var matchingString = strCompare.IndexOfAny(strStringContains.ToCharArray()) != -1;
              if (matchingString)
              {
                 
   
for(int i=0; i<=SEQ.Length; i++){
   
        if (DNA[i]=="A")
        {richTextBox1.AppendText("U");
        len++;
        }
                if (DNA[i] == "G")
                {richTextBox1.AppendText("C");
                len++;
                }
                        if (DNA[i] == "C")
                        {richTextBox1.AppendText("G");
                        len++;
                        }
       
                                if (DNA[i] == "T")
                {richTextBox1.AppendText("A");
                                len++;
                                }
                               
        }

---

This is where the trouble begins
right at the first if statement

Code:

---

for(int i=0; i<=SEQ.Length; i++){
   
        if (DNA[i]=="A")
        {richTextBox1.AppendText("U");
        len++;
        }
                if (DNA[i] == "G")
                {richTextBox1.AppendText("C");
                len++;
                }
                        if (DNA[i] == "C")
                        {richTextBox1.AppendText("G");
                        len++;
                        }
       
                                if (DNA[i] == "T")
                {richTextBox1.AppendText("A");
                                len++;
                                }
                               
        }

---

Quote:

---

Originally Posted by ApacheOmega

I originally wrote this code In C++ and the program looks a bit different and the array is a char array instead of a string array.

---

A string is effectively a char array, so you need a string for your DNA sequence.

In your code:

Code:

---

namespace bioinformaticsCal
{

    public partial class Form1 : Form
    {
        int numberOfCodons;
        int rnaLength;
        int beginIndex;
        int endIndex;
        int i;
        int j;
        int k;
        string[] codons = { "UUU", "UUC", "UUA", "UUG", "UCU", "UCC", "UCA", "UCG", "UAU", "UAC", "UAA", "UAG", "UGU", "UGC", "UGA", "UGG", "CUU", "CUC", "CUA", "CUG", "CCU", "CCC", "CCA", "CCG", "CAU", "CAC", "CAA", "CAG", "CGU", "CGC", "CGA", "CGG", "AUU", "AUC", "AUA", "AUG", "ACU", "ACC", "ACA", "ACG", "AAU", "AAC", "AAA", "AAG", "AGU", "AGC", "AGA", "AGG", "GUU", "GUC", "GUA", "GUG", "GCU", "GCC", "GCA", "GCG", "GAU", "GAC", "GAA", "GAG", "GGU", "GGC", "GGA", "GGG" };
        string[] aminoAcids = { "Phenylalanine", "Phenylalanine", "Leucine", "Leucine", "Serine", "Serine", "Serine", "Serine", "Tyrosine", "Tyrosine", "Stop", "Stop", "Cysteine", "Cysteine", "Stop", "Tryptophan", "Leucine", "Leucine", "Leucine", "Leucine", "Proline", "Proline", "Proline", "Proline", "Histidine", "Histidine", "Glutamine", "Glutamine", "Arginine", "Arginine", "Arginine", "Arginine", "Isoleucine", "Isoleucine", "Isoleucine", "Methionine", "Threonine", "Threonine", "Threonine", "Threonine", "Asparagine", "Asparagine", "Lysine", "Lysine", "Serineine", "Serineine", "Arginine", "Arginine", "Valine", "Valine", "Valine", "Valine", "Alanine", "Alanine", "Alanine", "Alanine", "Aspartate", "Aspartate", "Glutamate", "Glutamate", "Glycine", "Glycine", "Glycine", "Glycine" };
        string codon = "";
        string protein = "";
        string [] DNA;
       
        string RNA;
        string SEQ;
        int len;
      ...

---

You are declaring 'DNA' to be an array of strings, but you are not assigning any strings to this array. So when you come to reference them:

Code:

---

        if (DNA[i]=="A")

---

DNA[I] will be null.

But you are reading your text file into the SEQ variable anyway - so why aren't you comparing SEQ with the codons?

If the sequence is DNA I have to convert it to RNA first then I guess i compare then. Im not sure. Ill tweek it some more when I get back Home