How to print empty array elements / skip array elements in C?

Question

So I have 3 int type arrays, A, B and C. The program checks array A elements for prime numbers, if the number is prime in array it gets copied to array B, if not array C. Later it prints all three arrays.

This is the code piece a have problems with:

    if(onalg)
    {
    B[i]=A[i];  
    }
    else
    {
    C[i]=A[i]; 
    }

Then sort the array B and C using qsort ( done this, works ). After all that it has to print all arrays like this:

for(i=0;i<n;i++)
{
    printf("%d        %d        %d\n", A[i],B[i], C[i]);
}

How can I make it print empty spots in array? Currently it prints some random numbers in array C[i] spot when B[i]=A[i] and in array B[i] when C[i]=A[i].

Alok Save · Accepted Answer · 2011-12-11 11:25:36Z

1

You cannot.
You will need to assign some value to your array member which will indicate it is not initialized and then check for that value and treat it as blank while printing it out.

if(onalg)
{
    B[i]=A[i];  
    C[i]= //Some place holder value indicating unfilled;
}
else
{
    C[i]=A[i]; 
    B[i]= //Some place holder value indicating unfilled;
}

answered Dec 11, 2011 at 11:25

Alok Save

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2 Comments

Andr3az Over a year ago

What is that placeholder that indicates the array is unfilled? I have searched everywhere, can't find anything that can do that :S

Alok Save Over a year ago

@user1092141: Place holder means a value which you decide will never be a valid value in your array(say -999) and then you check that while printing to know when to print a blank.

Mat · Accepted Answer · 2011-12-11 11:27:37Z

1

Either initialize your arrays B and C before you start filling them in (with memset for instance), or set them both in each conditional.

if(onalg)
{
    B[i]=A[i];  
    C[i]=-1;  // or some other constant
}
else
{
    C[i]=A[i]; 
    B[i]=-1;  // or some other constant
}

If you don't have a constant you can use as a "guard", consider using two more arrays, properly initialized, that store whether that index in B and C resp. is set or not.

You'll need more logic in your display code either way to print out a blank for "unset" values.

answered Dec 11, 2011 at 11:27

Mat

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Comments

PeterP · Accepted Answer · 2011-12-11 11:29:02Z

0

CString strA, strB, strC;

for(i=0;i<n;i++)
{
    if (A.GetLength() > i+1)
        strA = Format(%d, A[I]);
    else
        strA = "";

    if (B.GetLength() > i+1)
        strB = Format(%d, B[I]);
    else
        strB = "";

    if (C.GetLength() > i+1)
        strC = Format(%d, C[I]);
    else
        strC = "";

    printf("%s        %s        %s\n", strA, strB, strC);
}

answered Dec 11, 2011 at 11:29

PeterP

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Comments

Panos · Accepted Answer · 2022-02-16 22:38:10Z

0

When you want it to be empty, you can set the B[i] or C[i] to 0, and then print it one by one by checking if the value is 0.

answered Feb 16, 2022 at 22:38

Panos

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1 Comment

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