C reference code

Im in intro to C right now and for the benefit of members wanting to learn the language I will post my assignments, they are made up by the teacher so im sure they will not be the same as anyone with the same class. Feel free to sticky this. Or tell me to shutup if you don't want it up

Any questions about the code post them.

Here's my first assignment. The comments should explain what it does

Code:

/***************************************************************************
 First assignment for intro to C By WookMaster
 Compiled with GCC under Linux using the Kdevelop IDE for project management
 For question email [email]wookmaster@techdefine.com[/email] or visit my website
 [url]www.techdefine.com[/url]
 ***************************************************************************/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

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

int main(void)
{
  	const double gallons_per_hour = 0.3; //Gallons per hour as given by assignment
	const double pi = 3.14159;           //The constant value of PI
	const double cc_per_gallon = 3785.4; //CC per gallon as defined by assignment
	double diameter = 30;		     //The diameter of the gas can
	double radius = diameter/2;	     //Dividing by 2 give the radius of the can
	double height = 45;	             //The height of the can	
	double volume;			     //A variable to be used to hold the volume of the can when computed
	double gallons;			     //A variable to hold the answer to how many gallons the can holds
	double total_time;		     //The variable to hold our final answer
    	/*Calculates the volume*/
	volume = ((pi) * (radius * radius)) * height;
	/*Turns the Volume into Gallons*/
	gallons = volume * cc_per_gallon;
	/*Calculates the total time the machine will Run*/
	total_time = gallons * gallons_per_hour;
	/*Prints out the answer*/
	printf("The total time the machine will run is: %6.2f\n", total_time);

  return 0;
}

 

it's cool man.. keep posting.

 

Why do you use autconf when you don't use any of it's features?

 

Kdevelop put it there and I forgot to remove it

 

To improve the quality, I would suggest that all your constants are made double precision rather than derived single precision or integer constants to prevent any loss of precision on calculations. Similarly your use of %6.2f for a double precision variable may produce a machine dependent result. There exists a constant pi in <math.h> or alternatively calculate it from 4 times arc tan of 1 radian. The printf function returns a value by default, what are doing with this value or if nothing cast the result to (void). Code formatting should be consistent, e.g., indentation. What units are your calculations in, imperial or metric - I would guess imperial.

Finally, what would you do if the constants were much larger or smaller and result in an overflow or underflow in result? etc.

 

What exactly is the supposed purpose of doing this? Sounds like ANSI stuff (can't be pre-ANSI due to the fact that it's void) but I've never really seen a point to this and -ansi -W -Wall -pedantic never complains about it. Personally I'm not a big fan of it as it just clutters space.

 

/***** Excuse me, but... I just wanted to say this is going to be a ***/
/***** Great thread for me, as I am trying to learn this stuff! (ThankYou all!) */

 

I'd probably change some stuff, your asking theoretical questions involving the code being different than it is. It works fine like this, theres something my teacher doesnt like but I havnt gotten to talk to him yet, Im hoping my math isnt off, I don't have the math memorized I looked it up online.


New assignment coming soon involving getting user inputted values.

 

whoops, math was wrong

Heres the corrected code for the first assignment

Code:

/* First Assignment Intro to C WookMaster */

#include <stdio.h>

int main (void)
{
	const double gallons_per_hour = 0.3;
	const double pi = 3.14159;
	const double cc_per_gallon = 3785.4;
	double diameter = 30;
	double radius = diameter/2;
	double height = 45;
	double volume;
	double gallons;
	double total_time;
    /*Calculates the volume*/
	volume = ((pi) * (radius * radius)) * height;
	/*Turns the Volume into Gallons*/
	gallons = (volume / cc_per_gallon);
	/*Calculates the total time the machine will Run*/
	total_time = (gallons / gallons_per_hour);
	/*Prints out the answer*/
	printf("The total time the machine will run is: %6.2f\n", total_time);
return 0;
}
	

 

The next version of this program, it uses scanf to get the user data for the size of the gas can

Code:

/*Intro to C By WookMaster
This accepts user input and calculates the amount of time in Hours a 
generator will run on a full tank of gas depending on the gas can dimensions.*/

#include <stdio.h>

int main (void)
{
	const double gallons_per_hour = 0.3;       //Initalizes a Constant value
	const double pi = 3.14159;			       //Initalizes a Constant value
	const double cc_per_gallon = 3785.4;       //Initalizes a Constant value
	double diameter = 0;                       //Initilizes a variable
	double height = 0;						   //Initilizes a variable
	double volume = 0;						   //Initilizes a variable
	double gallons = 0;						   //Initilizes a variable
	double total_time = 0;					   //Initilizes a variable
	
 
	printf("Please Input the height of the Can: " ); // Prints the preceding statement
	scanf("%lf", &height);		//Accepts Input for the Height of the can
	printf("\nPlease Input the Diameter of the can: ");
	scanf("%lf", &diameter);  //Accepts user input for the diameter
	double radius = diameter/2;   //Computes the Radius of the can at the same time initilizing a variable.
	volume = ((pi) * (radius * radius)) * height;  // Computes the volume of the can
	gallons = (volume / cc_per_gallon); //Computes the gallons that are in the can
	total_time = (gallons / gallons_per_hour);  // Calculates the hours the machine will run in hours.
	printf("The total time the machine will run is: %6.2f\n", total_time); //Print the answer
return 0;
}

Ive been told by declaring radius in the middle im using habits from my C++ coding, so FYI Its not stylin in C to do that.

 

It's not only "not stylin" but it will also not compile on any compiler that is pre-ansi, ansi, c89, and most likely everything else but c99.

 

compiled just fine under GCC.....

 

i think it's not just style. it's rather good to follow conventions in programming style. question: does that convention make the code more efficient? at least for c language... that i don't know. hehe.

 

Does this convention/rule stem from the fact that C is not quite as dynamic as C++. Or at least in the early days of C compilers things weren't as dynamic as modern compilers.

I mean it makes sense from that point of view for a compiler to force a function to declare all the heap memory it is going to need for its life time right at the beginning... Makes sense to me at least... That way the compiler can allocate it its memory and then worry about where the next function is and how much memory that needs.

Cheers,
Greg

 

gcc supports c99, though I'm not sure if it would by default

By a very very very small amount on compilers that dont optimize it, yes. But not enough that it'd make a visible difference if ran a billion times.

C has no knowledge of a heap, stack, or other "standard" data structure. That over, automatic declarations are not on the heap, that's dynamic and is not the exact same as this case. The heap usually stores static declarations and dynamic declarations usually done by an sbrk syscall to expand the heap. malloc and free depend on the heap. int foo; char bar; double baz; does not. And at that, if they did, there'd always be realloc.

There's no reason why a compiler should think about the next functions prerequisites. If it did, then there'd be an awful mess with branch prediction, function pointers, and signals. Each function should just allocate it's own memory and deallocate (sub esp, 0xf00 and add esp, 0xf00 aren't very large speed hits) by itself.

 

Now, that's an info! Great!

Thanks vlad.