average of an array

[mrsirpoopsalot]

I just want to calculate the average of an array
but i cant seem to get it to work right.

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  
  

  int x,c;
  int Array[5]={
      99,105,67,23,79
      };
   
  for ( x=0; x<5; x++ )
  Array[x]= Array[x]+ Array[x]/5;

 for(c=0;c<5;c++) 
  printf("average is %i\n",Array[c]);
  
  
  
  
  getchar();	
  return 0;
}

[Kennedy]

Think about how to do an average. If you have a list of numbers, say 1-10 and you want to average those numbers how would you do it on paper?

[cboard_member]

int Array[] = { 99, 105, 67, 23, 79 };
size_t Len = sizeof(Array) / sizeof(Array[0]); // If you didn't know it had 5 elements - a little trick for later :-)
int Sum = 0;

for ( int i = 0; i < Len; i++ )
  Sum += Array[i];

printf( "Average: %2.2f\n", Sum / Len );

Something like that if my maths doesn't fail me (it always does).

[Adak]

It's important to keep in mind how you do something by hand, and THEN write up the code.

If you just start "banging out code", you can expect many errors like this.

  for ( x=0; x<5; x++ )
  Array[x]= Array[x]+ Array[x]/5;

You need a sum, here. Add the array numbers all up. I can't wrap my head around whatever the above code is intending.

for(c=0;c<5;c++) 
  printf("average is %i\n",Array[c]);

How many averages are there for one array?

Just ONE, not 5.

Adak

[cboard_member]

>> It's important to keep in mind how you do something by hand, and THEN write up the code.

Indeed. Sorry mrsir - didn't think.

[mrsirpoopsalot]

i think what i was trying to do was take the contents in the array and add them together then / by 5 to get the average.

for ( x=0; x<5; x++ )
  Array[x]= Array[x]+ Array[x]/5;

im trying to learn c so i am going to make alot of mistakes! and i did think it out before i coded it. but it didnt help =/

it works:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 
 int x,c;
 float average;
 int Array[5]={
      99,105,67,23,79
      };
   
  for ( x = 0; x < 5; x++ )
  average += Array[x];
 
  printf("average is %.2f\n",average/5);
  
  getchar();	
  return 0;
}

thanks for all your help.

[Adak]

i think what i was trying to do was take the contents in the array and add them together then / by 5 to get the average.

for ( x=0; x<5; x++ )
  Array[x]= Array[x]+ Array[x]/5;

im trying to learn c so i am going to make alot of mistakes! and i did think it out before i coded it. but it didnt help =/

it works:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
 
 int x,c;
 float average;
 int Array[5]={
      99,105,67,23,79
      };
   
  for ( x = 0; x < 5; x++ )
  average += Array[x];
 
  printf("average is %.2f\n",average/5);
  
  getchar();	
  return 0;
}

thanks for all your help.

You sound quite sincere, (otherwise I'd not post this), so here comes some more tips:

Make your variable names, reflect what they do, as close as possible. Take this for example:

  for ( x = 0; x < 5; x++ )
  average += Array[x];

That's code, and it will work, but it's NOT PROgramming. The first thing I think of when I see that is "What's up with this variable "average"?
Now notice the difference:

  for ( x = 0; x < 5; x++ )
     sum += Array[x];

and EVERYBODY on the planet knows what "sum" is doing in this loop. As my old geometry teacher used to frequently complain:

"Oh No! Oh No, it's too easy!!"

And I really like the way you're using the += operator. THAT'S programming!

You could make this more useful in other programs by including a counter variable in place of the 5, like this:

  for ( x = 0; x < 5; x++ )  {
     average += Array[x];
     count++;
  }

Then it's easy to just code up:

printf("\n Average is: %.2f ", sum / count);

Ahluka showed another way to get the count of the numbers, if the array is full, above.

Anyway, I better stop this post. You are beginning to impress me. :P

Adak

[Mario F.]

Now, you impress me and tell me what is there that is still left to fix

[mrsirpoopsalot]

thanks for all the tips!
much appreciated

[Adak]

Now, you impress me and tell me what is there that is still left to fix

Oh sure, we could:

1) remove Stdlib.h, it's not needed
2) variable c is not needed.
3) by custom, the "x" should be replaced with an "i" in the for loop
4) lose the parameters to main - they're not needed.

"int main(void)" would be fine.

But it's a good start.

With these minor changes, it works in my old version of C - no warning, no errors, and correct answer (74.60).

Was there something else that jumped out at you as needing improvement, Mario?

Adak

[Mario F.]

Well, you are looking at an unitialized variable there. average, (or if the user followed your advise, sum) should be initialized before being used.

The result of average += Array[x]; is not guaranteed to be correct across compilers. Worst, without all warnings turned on, the compiler may not even warn about it. And some compilers don't warn no matter the case.

Also of note the fact that while the above default initializes average to 0f in my compiler (gcc 3.4.5 mingw special), it will definitely not do it if or when the code is upgraded to C++. And can be easily forgotten about.

[Richie T]

Well done Adak, I would change those too (although I mightn't be too fussy about using an x instead of an i), but you're missing what mario was probably hinting at - shouldn't average be initialised before you perform:

for ( x = 0; x < 5; x++ )
  average += Array[x];

Edit - beaten, but correct at least!

[dwks]

Rather than using 5 everywhere, in case you change the number of elements in the array, you can use this:

sizeof(Array) / sizeof(*Array)

You might want to put this in a #define or a variable.

You also don't have to put a size for the array, since you have an initializer; the compiler can calculate the size for you.

[Adak]

Rather than using 5 everywhere, in case you change the number of elements in the array, you can use this:

sizeof(Array) / sizeof(*Array)

You might want to put this in a #define or a variable.

You also don't have to put a size for the array, since you have an initializer; the compiler can calculate the size for you.

All good points.

In my little version, I just changed the for loop to:

for (i = 0, sum = 0; i < Asize; i++) , out of habit.

After reading about why it's preferred that way in K&R's book "The C Programming Language", year before last, I just made that a standard for myself.

Thanks for the notes, guys. I'm sure mrsir (whom I'm trying not to call "poopy", but it's hard to avoid with a handle like that) will now be able to refine his program, even more.

Adak

[disha11dec]

Array[x]= Array[x]+ Array[x]/5;

should be replaced by:

Sum=0;
for(x=0; x<5;x++)
Sum=Sum+Array[x];

Sum=Sum/x;