Thread: Trouble with sqrt ()

Here's a simple program that is to be used for calculating Sum, Average and Standard Deviation.

But it doesn't work. There's a problem with the sqrt function. I hear it returns a double value. But then there will be a pointer problem I guess. Pointer variables have to be int. (just guessing)

Here's the program:

Code:

/*
Write a function that receives 5 integers and returns the sum, average and standard
deviation of these numbers. Call this function from main() and print the results in main().
*/


#include<stdio.h>
#include<math.h>
main()
{
	int a, b, c, d, e, sum, avg, sd;
	int calc (int a, int b, int c, int d, int e, int *sum, int *avg,int *sd);

	printf("Enter Five Numbers:");
	scanf ("%d %d %d %d %d", &a, &b, &c, &d, &e);

	calc (a, b, c, d, e, &sum, &avg, &sd);
	
	printf("Sum=%d", sum);
	printf("Average=%d", avg);
	printf("Standard Deviation=%lf", sd);

}

calc (int a, int b, int c, int d, int e, int *sum, int *avg, int *sd)
{
	int calc_sd;

	*sum=a+b+c+d+e;
	*avg=(a+b+c+d+e)/5;
	
	/*To calculate Standard Deviation, first we have to calculate
	the mean average. Here n=5 .. Five Numbers and then calculate
	Standard Deviation by this formula:
	sqrt(((x1-mean)(x2-mean)....(xn-mean))/total numbers)*/
	
	calc_sd = ((a- *avg)*(b- *avg)*(c-*avg)*(d-*avg)*(e-*avg))/5;
	*sd= sqrt(calc_sd); //sqrt function must have only one variable in those braces. :(
}

Also, one more thing...

I used GCC, and the program won't compile on it.
It gave me warning / errors I never knew.

But then I tried MS Visual C++ IDE..it gives me warnings and the program compiles fine.
Except that the Standard Deviation thing doesn't work out properly..

So is it like GCC won't compile the programs if there are warnings?

Originally Posted by OnionKnight

No, an object pointed to by a pointer does not have to be an int. The pointer itself is an int though.

Okay..so do you mean that changing it to double will help?

Also give some more inputs on using the sqrt function.

You can have a pointer to any data type - even structs - just change your
function parameters to double *sum, double *avg (etc.) Also, in main, the
corresponding variables (sum, avg etc.) should be doubles as well.

Other things:

1. main returns int, see my sig.
2. your calc function should be prototyped before main , not in it.
3. Perhaps it would be a better idea to read your numbers into an array, as
opposed to 5 separate variables
4. sqrt () accepts a double parameter as well

5. >>You don't have to change your ints if you're happy with them.

why? If I was writing this, I would use doubles exclusively, using ints is just
going to involve type casts and possible data loss - i'd read in 5 doubles and
determine their average and use sqrt - keeping all the types the same.

Originally Posted by Richie T

1. main returns int, see my sig.

Unadorned main, while bad form, defaults to int, so it is technically okay. Actually since any unprototyped function defaults to int foo(...), his calc() is supposed to return an int, but doesn't. That's bad. Make it a void function.

C99 is for the most part upward-compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. The C standards committee decided that it was of more value for compilers to diagnose inadvertent omission of the type specifier than to silently process legacy code that relied on implicit int. In practice, compilers are likely to diagnose the omission but also assume int and continue translating the program.

From Wikipedia

And I agree with them!

Yeah, but both his compilers default to C89 mode, so.

And I'm certainly not advocating using unprototyped and untyped functions, if that's what you're implying.

> printf("Standard Deviation=%lf", sd);
You're trying to print an int as a float (not that %lf is a valid format, just %f will do)

>>Yeah, but both his compilers default to C89 mode, so.

Be that as it may, it's still a good idea for the OP to be aware of potential issues
with his code - he should write standard, portable code, not whatever his
compiler lets him get away with. Granted, C99 isn't very widely supported,
but it's the most up to date standard we have, so it's foolish to C89 forever,
especially when it allows poor code like this. I've nothing further to add, unless
the OP has more questions.

I am learning and haven't yet dealt with arrays..so I have to make the program without arrays for the time being.

@ssharish2005

Thanks for pointing it out. (Logic is incorrect)
I think I forgot to take the square of the terms.

I will change my Logic accordingly now.

Also, I was taught that its okay to declare the function prototype inside main.
You fellas seem to do it the other way..declaring it outside main.
I wonder if that causes much of a difference.

@Salem
Thanks for pointing it out.
I had read somewhere that %lf is the format specifier for double!
Now I verified whether that was correct.
I understand now that the format specifier for double is %e and %Lf is for Long Double!

@Richie T and zx-1
Talking about C89 and C90...
Hehe.your talks are abysmal for me.
Not sure I understand that!
I am also using Microsoft Visual Studio C++ by the way.