An Array of Classes

This is a discussion on An Array of Classes within the C++ Programming forums, part of the General Programming Boards category; I need to create an array of classes; something like; I have a class named calculate, and I need to ...

  1. #1
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    An Array of Classes

    I need to create an array of classes; something like; I have a class named calculate, and I need to create an array of the class like:

    claculate array[1000];

    is that possible? I tried this...and it compiles alright....but when I run the program...it gives a segmentation fault. Please suggest how I can do this!!


    Thanks

    Shrestha

    Here is a snippet of what I need to do:



    Code:
    calculate operator *(calculate big1, calculate big2)
    	{
    	calculate ans[1000];
    
    	int temp=0;
    	int temp1=0;
    	int temp2=0;
    	for (int i=1; i<big2.count+1;i++)
    	   {
    		for(int y=big1.count; y>0; y--)
    		{
    		   temp1=big1.array1[y]*big2.array1[i]+temp;
    		   temp=0;
    		   if (temp1>9)
    			{
    			   temp=temp1/10;
    			   temp1=temp1-temp*10;
    			}
    		   ans[i].array1[y]=temp1;
    		}
    	   ans[i].count=big1.count;
    	
    	   if (temp != 0)
    		{
    		  for (int j=ans[i].count+1; j>0; j--)
    			{
    			ans[i].array1[j]=ans[i].array1[j-1];
    			}
    		  ans[i].array1[1]=temp;
    
    		ans[i].count++;
    		}
    
    //This is the part where I'm not so sure
    
    	   for (int I=1; I<(big2.count-i+1); I++)
    		{
    		  ans[i].array1[ans[i].count+I]=0;
    		}
    	   ans[i].count=ans[i].count+(big2.count-i);
    
    
    ans[0]=ans[0]+ans[i];
    	   }
    
    
    return (ans[0]);
    	}
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  2. #2
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    Code\

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  3. #3
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    yes, you can make an array of user defined class objects.
    Code:
    class calculations
    {
       //whatever;
    };
    
    int main()
    {
      calculations ans[1000];
      //etc.
    }
    but there are several techincal hitches. First an array of any size at all, particularly if the objects are of any significant size, will eat up your stack space, so it may be best to use the free store instead. Second, the compiler will use the default constructor when creating each calculations declared in the array, so you have to have a default constructor available--either by using the default default constructor the compiler will provide if you don't declare any other constructors, or, preferably by declaring and implementing your own default constructor.

  4. #4
    Guest Sebastiani's Avatar
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    It's hard to say, not knowing the details of the calculate class. But look at this:

    for (int i=1; i<big2.count+1;i++)

    If big2.count is how many items in an array, then you will surely overwrite memory by going to big2.count+1. Look at an array:

    int array[1000];

    The first index is '0', not '1'. And the last index is '999', not '1000'.

    The rule of thumb for all arrays is:

    "Don't access higher than count - 1."

    So change these to:

    for (int i = 0; i < (big2.count - 1); i++)

    for(int y = (big1.count - 1); y > 0; y--)


    My next advice is to build up the function slowly, adding more code little by little. Once you verify that the current snippet works, add more code. This will make debugging easier.



    ITSA
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  5. #5
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    Wink An Array of Classes

    Thanks for the reply...I found out the error.....well...I just decreased the size of the array to 100 instead of 1000 and it worked!! Thanks for all the help though!!!!!


    PEACE!!!
    Manish

  6. #6
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    sounds like you were filling up the variable stack with the array of size 1000. If you want to use that size of an array, then you will need to reset the size of the variable stack, or more commonly, use the free store/heap/dynamic memory to store all the variables.

  7. #7
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    You might also be interested in using the stl containers such as <vector>.

  8. #8
    Code Goddess Prelude's Avatar
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    >You might also be interested in using the stl containers such as <vector>.
    Yes, if you have the option (ie. You're not doing homework), then STL containers are preferable to anything hand coded.

    -Prelude
    My best code is written with the delete key.

  9. #9
    Guest Sebastiani's Avatar
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    Yes, if you have the option (ie. You're not doing homework), then STL containers are preferable to anything hand coded.

    bah!



    ITSA
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  10. #10
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    You also might want to look into the MS helper class CObjectArray on the mdsn helpfiles. It is wery nice and easy to work with.

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