Thread: trying to do simple math with float and int type

I'm trying to learn by doing. I have written some code below and it's not outputting the way I expected it to. Once I get this piece working I'd like to add code to round the numbers so that there are only 2 to 3 decimal places.

the step after that would be to add code so that I can leave z as an int type and then change it's type in function div()

if you could help out I'd really appreciate it, also if you have any suggestions or areas where I could potentially be shooting myself in the foot I'd appreciate the feedback as well


my code looks like this:

Code:

#include <stdio.h>

int x,y;
float z,a;

int mult(int x,int y);
float div(int x,int y);

int main()
{
	printf("\nPlease enter a number: ");
	scanf("%d",&x);
	printf("\nPlease enter a second number: ");
	scanf("%d",&y);
	
	a=mult(x,y);
	printf("\n%d times %d equals %f",x,y,a);

	printf("\nand");
	
	a=div(x,y);
	printf("\n%d divided by %d equals %f",x,y,a);
	
	printf("\nHave a nice Day!!!\n");
	
	
	
	
	
	return 0;
}



int mult(int x,int y)
{
	z=x*y;
	return z;
}

float div(int x,int y)
{
	z=x/y;
	return z;
}

and the output looks like this

Code:

Please enter a number: 5

Please enter a second number: 4

5 times 4 equals 20.000000
and
5 divided by 4 equals 1.000000
Have a nice Day!!!

I'm trying to allow variables 5 and 4 to be integers and z and a to be float. I expect the output to look like this

Code:

Please enter a number: 5

Please enter a second number: 4

5 times 4 equals 20.000000
and
5 divided by 4 equals 1.250000
Have a nice Day!!!

The catch is that 5/4 actually is 1 (well, 1 remainder 1, but you didn't ask for the remainder part). If you cast the numbers to float, and then divide, good things may happen.

do I need to cast x and y as float type to get the decimal place?

Originally Posted by vart

Why are you working with global variables?
and yes - to make float division you need to cast at least one of operands to float before you divide

because I don't know any better, this is really like my first attempt at a program all on my own.

The biggest problem I am having is variables act differently depending on how you save them with the %d, %f etc. its pretty annoying because I'm not 100% with what I'm doing and the limitations yet.

can anyone point me to a good example of casting?
also how do I limit decimal places on a float type variable?

thanks

1. Something like (float)x/(float)y is probably literally the only good example of casting that there is, since by the time you reach the level where you need some other form of casting you'll already have all the skills. And for that matter, this cast is unnecessary too: I usually do x*1.0/y which does the same thing.
2. What do you mean by "limit decimal places"? If you mean when printing the number out, then at some point you need to actually read the section on printf in your C book, or type "man printf" at your terminal/web browser. If you mean when storing the number, then there is of course no such thing (all floats are going to use the same amount of space internally no matter what).

Elysia-I know this may be beneath you explaining but, while I think I understand the idea of local module and global how am I supposed to make my program work if my variable don't work throughout the entire program(global? right) I am using the same variables in all of the program so how could I make this work without a global variable?

tabstop-I don't care what they store as. I want the values printed to show 2 decimal places. Will man printf give what I need to figure this out?

Thanks you guys are all pretty awesome. I know some of these questions must seem really mundane but I'm pretty much doing this on my own so you guys are much appreciated

And yes, man printf (or whatever reference you have to hand) will tell you how to print to a given precision (key word italicized for your pleasure).

Originally Posted by Elysia

So, say one function gets input. You pass the proper arguments for the function to store the data inside.
Then you pass that input to the next function, and then the next, etc. They will all be local then (but beware of pointers), but you get to pass information around your program as necessary.

There is no reason to "beware of pointers;" they are not treated differently than any other variable if we are discussing implications of local scope. Copies of pointers are generated if they are arguments to functions, too.

As for the variables. They do not actually work differently depending on what format specified (ie %d) you use. Actually it's more of the thing that C is dumb. It does not know what type you're passing to functions, so you must explicitly tell printf what type of arguments you're passing. If you specify the wrong type, then printf will give you wrong output because you lied to it.

Absolutely C knows the types of variables passed to functions because that information is available from the parameter list. The only contexts in which it isn't available include variadic functions (such as printf) and macro functions. Just wanted to clear that up, since this piece of advice is more about printf than it is about C or variables in general.

Furthermore, printf does work differently depending on the format: consider the differences between %o and %x, which print a number in octal and hexadecimal respectively.

OP, if you're still reading this, printf's help file will contain everything you ever wanted to know about using printf, including printing to the hundredths place and so forth.