Question

main()    
{    
    ....

    i = index;                
    while (i < j)    
    {    
    if (ip[i] == "/")    
      {    
        ip[i - 1] = (double.Parse(ip[i - 1]) / double.Parse(ip[i + 1])).ToString();

        for (int k = i; k < (ip.Length - 2); k++)
        {
          ip[k] = ip[k + 2];
        }

        Array.Resize(ref ip, ip.Length - 2);       
        j = j - 2;      
        i--;    
      }    
     i++;    
    }    
}

For the above code I wanted to apply Oop’s concepts.

This pattern repeats almost 5 times (for div,mul,add,sub,pow) in main program, with four identical lines .

To decrease the no of lines and there by to increase efficiency of code, I wrote the same like this.

i = index; 

while (i < j)

    {    
     if (ip[i] == "/")    
     {    
      ip[i - 1] = (double.Parse(ip[i - 1]) / double.Parse(ip[i + 1])).ToString();    

      ext.Resize(ip, i, j);  
     }    
     i++;    
    }


class ext
{
  public static void Resize(string [] ip, int i, int j)    
    {

      for (int k = i; k < (ip.Length - 2); k++) { ip[k] = ip[k + 2]; }    
      Array.Resize(ref ip, ip.Length - 2);    
      j=j-2; i--;    
      return  ;      
    }     
}

Code got compiled successfully. But the problem is the changes in array and variables that took place in called function are not reflecting in main program. The array and variables are remaining unchanged in main program.

I am unable to understand where I went wrong.
Plz guide me.

Thank You.

Answer 1

I don’t think you understand what ref parameters are for – once you understand those (and the fact that arrays themselves can’t change in size), you’ll see why Array.Resize takes a ref parameter. Have a look at my parameter passing article for details.

You can fix your code by changing it like this:

public static void Resize(ref string [] ip, ref int i)    
{
    for (int k = i; k < (ip.Length - 2); k++)
    {
        ip[k] = ip[k + 2];
    }    
    Array.Resize(ref ip, ip.Length - 2);    
    j = j - 2;
    i--;
}

and calling it like this:

ext.Resize(ref ip, ref i);

However, I suspect that using a more appropriate data structure would make your code clearer. Is there any reason you can’t use a List<string> instead?