Hi, could someone help me with arrays?

Hi. I am goodn. i hope to contribute helpfully to your board later, but right now I am the one in need of help. In my c class we are starting to go over Arrays. I really have no grasp of them, other than knowing

int[5] = {4, 6, 7, 2, -1}

is an array of size 5 with values 4, 6, 7, 2, and negative 1. I don't understand their application into programming at all. The way I tend to learn things is by seeing an example, but my prof. doesn't supply any.

Anyway, an assignment I have is to make a tone of functions in a header file using arrays such as isum, dsum, iaverage, daverage, imin, imax, dmin, dmax, etc.

I think if I could get a push in the right direction I would easily be able to do this. If someone could be so kind as to show me how one would do

Code:

---

isum
This function will take an integer array of numbers and the array size as its parameters.
It will return the sum of all the numbers in the array as an integer.

---

then I think I could do the rest no problem. I've already done very similar functions without arrays, so if someone could give me a start, I'm sure I could do the rest with arrays. I'll post my progress back here. Thanks.

Think of an array as a container for objects of the same type. That's it. A word such as "Word" is simply an array of 4 characters. However, arrays of characters are always ended with the '\0' (always considered a single character), and so the above array would actually be 5 cells long.

Arrays of integers are useful too since you can easily move through them with loops.

An example of an averaging function would be one that adds up the total of each cell and then divides that by the number of cells. Hence,

int box[5] = {5,9,10,62,77}; //<---An array of 5 integers

int i= 0;
int total = 0;
int avg = 0;

for( i=0; i< 5; i++)
{
total = total + box[i];
}

avg = total / 5;



Since arrays always start at "0"(not "1"), the adding stops after cell #4 is reached(so not cell# 5); If you accidentally access too many cells, your program will probably crash.


Anyway, that's one example.

> Think of an array as a container for objects of the same type.
> That's it. A word such as "Word" is simply an array of 4
> characters. However, arrays of characters are always ended
> with the '\0' (always considered a single character), and so the
> above array would actually be 5 cells long.

This is not always correct. Yes, you think of strings as being 'null
terminated', but it is not a requirement. It is if you are using most
of the 'str*' functions, but it isn't a requirement:

Code:

---

char array[4] { 'w', 'o', 'r', 'd' };  // This is legal.

strncpy( array, 4, "cows" ); // This is legal.

puts( array ); // This is bad in this case.

---

Generally speaking, yes, you want all of your 'strings' to be null terminated.

A 'string' is an array of characters that is terminated by 1 character which has the value of zero. Thus:

char array[5] = "word";

This will null terminate it for you becuase you're using a "string". By enclosing the characters in double quotation marks at the point of assignment, it adds the null terminator. In my example, since I assign each character seperately, it will not.

Quzah.

a hint on isum is that your function declaration would look like this:

int isum( int nNum[], int nQty );

I knew all about what they meant, and about the 0 thing, and I also knew how to declare functions, but now I understand that about how about the box[i] thing. I see how I can increase the function.

so I could use

Code:

---

int isum (int iarr[], int num)
{
  int i, total;

  for (i=0, total=0; i < num; i++)
        {
          total += iarr[i];
          }
  return total;
}

---

As my isum function, would that be correct?

Right. That'd work. You can think of each element of an array like a drawer in a dresser. Or a row on a shelf. Something like that. Thus, when you want to access an individual element in the whole array, you're looking at 1 drawer in the dresser. Or one row on the bookshelf. So if you want to see what's on the third row, you do:

shelfContents = myShelf[2]; //since you start at 0 and work up

Yeah, you've got the hang of it.

Quzah.

Code:

---

int isum (int iarr[], int num)
{
  int i, sum;

  for (i=0, sum=0; i < num; i++) total += iarr[i];
  return sum;
}

int dsum (double darr[], double num,)
{
  double d, sum;

  for (d=0, sum=0; d < num; d++) total += darr[d];
  return sum;
}

int iaverage (int iarr[], int num)
{
  int i, sum, avg;

  for (i=0, sum=0, avg=0; i < num; i++) total += iarr[i];
        avg = total/i;
  return avg;
}

int daverage (double darr[], double num)
{
  double d, sum, avg;

  for (d=0, sum=0, avg=0; d < num; d++) total += darr[d];
        avg = total/d;
  return total;
}

---

Ok, here are my other functions so far. I'm having a little problem with my imax, though.

Code:

---

int imax (int darr[], int num)
{
        int i, max;
       
        for (max = -36667, i = 0; i < num; i++)
        {
        if (/*what would go here?*/ > max)
                max = /*what would go there?*/;
        }
        return max;
}

---

What would I put where my comments are?

Also, since I can't compile a header file, does anyone see any horrible errors with my other functions?

[code]int imax (int iarr[], int num)
{
int i, max;

for (max = -36667, i = 0; i < num; i++)
{
if (iarr[i] > max)
max = iarr[i];
}
return max;
}

duh, I don't know why I missed that. One thing I just noticed however is that I never defined num anywhere. I don't see how that could have happened, but how do I know num is the right number for i(or d) to be approaching?

One thing to consider about all of your function, is numeric overflow. Consider the following:

int array[3] = { 1000000000, 1000000000, 10000000000 };

Now try and add all those together in an 'int'.

Additionally, you could assign initial values for your variables when you declare them, and you wouldn't have to do it in your for loop. Either way works:

Code:

---

nt isum (int iarr[], int num)
{
  int i=0, sum=0;

  for (; i < num; i++) total += iarr[i];
  // or
  // while( i < num ) total += iarr[i++];
  return sum;
}

---

For a max function, first off, your value is likely wrong. If you are compiling on a 32 bit compiler, then an integer's max is ~2 billion.

Anyway, this is the check you would use in your case, assuming 16bit integers:

Code:

---

int imax (int darr[], int num)
{
                // I am assuming that this function returns the
                // integer in the array that is the highest?
        int i, max;
       
        for (max = -36667, i = 0; i < num; i++)
        {
                  if( num[i] > max ) max = num[i];
        }
        return max;
                // if you want to return the index of 'max', then
                // you'll need an additional variable to store the
                // value of 'i' at the time you find 'max'. Set this
                // when you set max as I've shown above.
                // { max = num[i]; maxIndex ] i; }
                // then later, 'return maxIndex;'
}

---

Quzah.

I also just noticed I was using int for my double functions, and I was using double variables in ones that should be integers.

for instance darray[d] where d is a double. Where in the world will a location in your array be 9.5? Heh, I changed those to integers(keeping the arrays as doubles, of course).

Quote:

---

Originally posted by Unregistered

Code:

---

int imax (int darr[], int num)
{
                // I am assuming that this function returns the
                // integer in the array that is the highest?
        int i, max;
       
        for (max = -36667, i = 0; i < num; i++)
        {
                  if( num[i] > max ) max = num[i];
        }
        return max;
                // if you want to return the index of 'max', then
                // you'll need an additional variable to store the
                // value of 'i' at the time you find 'max'. Set this
                // when you set max as I've shown above.
                // { max = num[i]; maxIndex ] i; }
                // then later, 'return maxIndex;'
}

---

Quzah.

---

I'm not quite sure what you mean, but are you forgetting that the initialazation of the for loop only happens once or something? I don't understand why I need another variable.

And where did num[i] come from? wouldn't you use iarr[i], the array you declared in the top?

No, I am aware that initialization happens once. What I'm saying is this:

Do you want to return the highest value, or the array index (ie: where the highest value is located at in the array)?

If you want to return the highest value, you can just return it like the function states. If you want to return the _INDEX_ of the value, then you need to keep tabs on that by using another value:

Code:

---

int imax (int darr[], int num)
{
        int i, max, index=-1;
       
        for (max = -36667, i = 0; i < num; i++)
        {
                  if( num[i] > max ) { max = num[i]; index = i; }
        }

                // this would return the index of the highest value
                return i;

                // this would return the actual highest number
                return max;
}

---

Thus:

int array[4] = { 200, 14, 703, -25 };
int highestValue;
int highestValueIndex;


highestValueIndex = imax( array, 4 );
printf("The highest value is located at array[%d] and is %d",
highestValueIndex, array[highestValueIndex );

// assume we used the second return statement instead
highestValue = imax( array, 4 );
printf("The highest value is located at array[%d] and is %d",
//Ooops! We don't know where it's at!
, array[highestValueIndex );


See what I was getting at?

Quzah.

edit: that first return should be "return index", sorry. I really should find my password so I can sign in...

Quzah.

OH. I see now. Yeah, I definitely want to return the highest value, not the index. Thanks for the tip though, I have a function in my next assignment which DOES need the highest index.

Quote:

---

Originally posted by goodn
[code]int imax (int iarr[], int num)
{
int i, max;

for (max = -36667, i = 0; i < num; i++)
{
if (iarr[i] > max)
max = iarr[i];
}
return max;
}

duh, I don't know why I missed that. One thing I just noticed however is that I never defined num anywhere. I don't see how that could have happened, but how do I know num is the right number for i(or d) to be approaching?

---

Yes, you declared num -- you declare it as a parameter to the function in the function definition.

So:

int imax(int iarr[], int num)

declares two variables -- one an array of ints named iarr, one an int named num. Whatever you pass in as your second parameter becomes num within this function.

So, if you called it like this:

imax(array,5);

num would be 5. If you called it like this:

imax(myArray,x); //x is an int

then num would have whatever value x had.

Ok, thanks. One other thing, it seems a lot of you put "//comment" for comments?

Isn't the proper way for comments to be /* comment */?
wouldn't // just screw your progam up?(I really don't use comments very often)

// is a C++ style comment.

/* */ is a C-style comment (also supported in C++).

*Some* C compilers will allow // in C code, but many will not, so you should never use it if you're programming in C.

Shame on all those people for using // on the C board :D

Heh, my professor has done the same thing on his web page! Shame on him!

isum
This function will take an integer array of numbers and the array size as its parameters.
It will return the sum of all the numbers in the array as an integer.

dsum
This function will take a double array of numbers and the array size as its parameters.
It will return the sum of all the numbers in the array as a double.

iaverage
This function will take an integer array of numbers and the array size as its parameters.
It will return the average of all the numbers in the array as a double.

daverage
This function will take a double array of numbers and the array size as its parameters.
It will return the average of all the numbers in the array as a double.

imax
This function will take an integer array of numbers and the array size as its parameters.
It will return the largest number in the array.

dmax
This function will take a double array of numbers and the array size as its parameters.
It will return the largest number in the array.

imin
This function will take an integer array of numbers and the array size as its parameters.
It will return the smallest number in the array.

dmin
This function will take a double array of numbers and the array size as its parameters.
It will return the smallest number in the array.

isort
This function will take an integer array of numbers, the array size and a sort value as an integer as its parameters.
This function will sort the array elements in descending order if the sort value is 0.
This function will sort the array elements in ascending order if the sort value is anything else.
This function does NOT return any value.
dsort
This function will take a double array of numbers, the array size and a sort value as an integer as its parameters.
This function will sort the array elements in descending order if the sort value is 0.
This function will sort the array elements in ascending order if the sort value is anything else.
This function does NOT return any value.

isearch
This function should take an integer array as its first parameter, array size as the second parameter, and a search key as the third parameter.
It will return the location number of the search key in the array, if it is found.
If it is not found in the array, it should return -999.
dsearch
This function should take a double array as its first parameter, array size as the second parameter, and a search key as the third parameter.
It will return the location number of the search key in the array, if it is found.
If it is not found in the array, it should return -999.

Code:

---

int isum( int[], int );
int iaverage( int[], int );
int imax( int[], int );
int imin( int[], int );
int isort( int[], int );
int isearch( int[], int, int );
double dsum( double[], int );
double daverage( double[], int );
double dmax ( double[], int );
double dmin ( double[], int );
double dsearch( double[], int, double );
double dsort ( double[], int );


int isum (int iarr[], int num)
{
  int i, sum;

  for (i=0, sum=0; i < num; i++) sum += iarr[i];
  return sum;
}

int dsum (double darr[], double num,)
{
  double sum;
        int i;

  for (i=0, sum=0; i < num; i++) sum += darr[i];
  return sum;
}

int iaverage (int iarr[], int num)
{
  int i, sum, avg;

  for (i=0, sum=0, avg=0; i < num; i++) sum += iarr[i];
        avg = sum/i;
  return avg;
}

double daverage (double darr[], int num)
{
  double sum, avg;
        int i;

  for (i=0, sum=0, avg=0; i < num; i++) sum += darr[i];
        avg = sum/i(double);
  return avg;
}

int imax (int iarr[], int num)
{
        int i, max;
       
        for (max = -36667, i = 0; i < num; i++)
        {
        if (iarr[i] > max)
                max = iarr[i];
        }
        return max;
} 

double dmax (double darr[], int num)
{
        int i;
        double max;
       
        for (max= -100000, i=0; i < num; i++)
        {
        if (darr[i] > max)
                max = darr[i];
        }
        return max;
} 

int imin (int iarr[], int num)
{
        int i, min;
       
        for (min = 36667, i = 0; i < num; i++)
        {
        if (iarr[i] < min)
                min = iarr[i];
        }
        return min;
}

double dmin (double darr[], int num)
{
        int i;
        double min;
       
        for (min= 1000000, i=0; i < num; i++)
        {
        if (darr[i] < min)
                min = darr[i];
        }
        return min;
} 

int isort(int iarr[], int num)
{
  int temp, pass , i;

  for (  pass = 0; pass < num - 1; pass++ )
  {
      for ( i = 0; i < num - pass - 1; i++ )
      {
        if ( iarr[ i ] > iarr[ i + 1 ] )
                {     
            temp = iarr[ i ];               
            iarr[ i ] = iarr[ i + 1 ];
            iarr[ i + 1 ] = temp;
        }
      }
  }
  for ( i = 0; i < num; i++ )
      return iarr[];
}

double dsort(double darr[], int num)
{
        double temp;
  int pass, i;

  for (  pass = 0; pass < num - 1; pass++ )
  {
      for ( i = 0; i < num - pass - 1; i++ )
      {
        if ( darr[ i ] > darr[ i + 1 ] )
                {     
            temp = darr[ i ];               
            darr[ i ] = darr[ i + 1 ];
            darr[ i + 1 ] = temp;
        }
      }
  }
  for ( i = 0; i < num; i++ )
      return darr[];
}

int isearch(int iarr[], int sizeofArray, int key )
{
  int n;
  for ( n = 0; n < sizeOfArray; n++ )
  {
      if ( iarr[ n ] == key )
        return n;
  }
        return -999;
}

double dsearch( double darr[], int sizeofArray, double key )
{
  int n;
  for ( n = 0; n < sizeOfArray; n++ )
  {
      if ( darr[ n ] == key )
        return n;
  }
        return -999;
}

---

Ok, there are the specifications for my header file, and there IS my header file. Will my functions work? Could someone pretty please make me a test c program to test all the functions?

Here's a good question: Why don't you try it?

Honestly. You wrote them, you know what is expected of them. You must have tested them (right? You _did_ test them?), so it should be a simple task to write a program to try them out.

While I do tend to be helpful, I don't see it my place to compile and try every program every person puts up. So don't take it personal. If you're having problems, I can see where you'd be posting for help. But just to have some one test a function? Why can't you?

Quzah.

Problem solved.