int[] str = new int[100]; 

            for (int k = 0; k < textBox1.Text.Length; k++)
            {
                string z=textBox1.Text;

                str[k] = textBox1.Text.IndexOf(z,k);  //this should put str[0]=textbox1.text[0]

label1.Text = Insertion.insert(textBox1.Text);

class Insertion
    {
        public static string insert(string x)
        {

private void Form1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (label1.Text.Length <= 15)
            {
                switch (e.KeyChar)
                {
                    case '1':
                        label1.Text += e.KeyChar.ToString();
                        break;
                    //... etc

for (int i = 0; i < 10; i++) 
      {
          printf("%d\n",i);
      }