how to remove item from array

[cannsyl]

I have the function removing items from position 0, but it won't remove items past that, and I don't know why...does anyone else see the problem? I have a dynamic parallel array in which a distinct number is entered into data[i] and copies of that number are tracked by freq[i] so when I remove one freq[i] is decremented and if freq[i] goes to 0 then the array is shifted to reflect the new smaller array size. Here is what I have so far...

bool IntStore::remOne(int target)
{
    for(int i = 0; i < used; i++)   //start loop to go through arrays to find target number
    {
       
       if (data[i] == target)  //if data[i] == target decrease freq[i] by one
       {
                 
          freq[i]--;
       }
                    
       if (freq[i] == 0)  //if freq[i] == 0 shift array down and resize array
       {
          
          for (int j = i; j < used; j++) //start loop to shift array
          { 
             data[j]= data[j+1]; //move data down one
             freq[j] = freq[j+1]; //move freq down one
             used--;  //update used to reflect the removed number
             resize (capacity - 1);  //resize capactity to reflect the smaller array
          }
          
          return true;  //if a copy has been removed if freq == 0
                 
       }
          
       return true;  //if a copy has been removed
                                      
    }
         
    return false;//if a copy has not been removed

}

[jsmith]

You do not want to do any of the code inside the if() on line 12 if data[i] != target, right?

[cannsyl]

right

[jsmith]

.... but you are. So does that fix it?

[cannsyl]

No that didn't fix it

[mcleano]

He's saying that what you don't want to do you are actually doing.

[cannsyl]

Right, I get that, so I changed it to

if (data[i] == target)  //if data[i] == target decrease freq[i] by one
       {
                 
          freq[i]--;
       //}
                    
       if (freq[i] == 0)  //if freq[i] == 0 shift array down and resize array
       {
          
          for (int j = i; j < used; j++) //start loop to shift array
          { 
             data[j]= data[j+1]; //move data down one
             freq[j] = freq[j+1]; //move freq down one
             used--;  //update used to reflect the removed number
             resize (capacity - 1);  //resize capactity to reflect the smaller array
          }
          
          return true;  //if a copy has been removed if freq == 0
          }       
       }

but it still doesn't work.

[jsmith]

Why are you decrementing "used" each time through the loop? Shouldn't
you just be decrementing it by one?

[cannsyl]

so should I move used outside the loop?

if (data[i] == target)  //if data[i] == target decrease freq[i] by one
       {
                 
          freq[i]--;
       //}
                    
       if (freq[i] == 0)  //if freq[i] == 0 shift array down and resize array
       {
          
          for (int j = i; j < used; j++) //start loop to shift array
          { 
             data[j]= data[j+1]; //move data down one
             freq[j] = freq[j+1]; //move freq down one
             resize (capacity - 1);  //resize capactity to reflect the smaller array
          }
          used--;  //update used to reflect the removed number

          return true;  //if a copy has been removed if freq == 0
          }       
       } 

[jsmith]

Did you also want to resize it every time through the loop, or just once?

Does it work as is? I'm guessing the above comment won't necessarily cause a problem, but will
reduce the efficiency. However, I'm also guessing that it still doesn't quite work because it looks
like you've got an off-by-one error inside the loop:

If used = 10, then the valid array indices are 0...9 inclusive. Since the loop on line 10 will execute
from i up to 9 inclusive, lines 12 and 13 appear to access the element at index 10, which is outside
the valid bounds.