What's wrong with this code?

I'm a beginner. This is an example code from my book and it keeps producing a warning (warning C4244: '=' : conversion from 'double ' to 'float ', possible loss of data):

Code:

#include <stdio.h>
#include <string.h>
#define DENSITY 62.4
int main()
{
	float weight, volume;
	int size, letters;
	char name[40];

	printf("Hi! What's your first name?\n");
	scanf("%s", name);
	printf("%s, what's your weight in pounds?\n");
	scanf("%f", &weight);
	size = sizeof name;
	letters = strlen(name);
	volume = weight / DENSITY;
	printf("Well, %s, your volume is %2.2f cubic feet.\n", name, volume);
	printf("Also, your first name has %d letters,\n", letters);
	printf("and we have %d bytes to store it in.\n", size);
	return 0;
}

Can someone please tell me what the problem with this code is? I've looked it over carefully and I can't find out what's wrong with it.

The problematic line is here:

Code:

#define DENSITY 62.4

The preprocessor replaces text matching DENSITY with the text 62.4. The compiler then analyzes this. The line read by the compiler is thus:

Code:

volume = weight / 62.4;

Now, in an expression, the type of the result is the type of the longest, floatiest operand. The type of weight is float, but the type of a floating-point literal is double. double is floatier(*) than float, so the result of the expression weight / 62.4 is double. You then attempt to assign a temporary value with the type double to a variable of type float. This is an assignment of a wider type to a narrower type and requires a diagnostic.

The solution is to either cast the result of the expression to (float), or cause the floating-point literal to be float by appending F or f:

Code:

#define DENSITY 62.4f

(*)

floatiest
floatier

You could also say it has higher/highest precision...

>You could also say it has higher/highest precision...
My way is more fun though.

Oh, ok. Thanks! I wonder why my book didn't cover this

>I wonder why my book didn't cover this
It your book is worth anything it will cover this when describing floating-point constants and type conversion rules.

K&R2 covers it in section 2.3, page 37 and section 2.7, page 42.