Circles Anyone?

[Nightsky]

I'm trying to do this problem but am stuck once again.
The problem basically states

"Write a program that reads in the radius of a circle and prints the circle's diameter, circumference and area. use the constant value 3.14159 for pi. Perform each of these calculations inside the printf statements and use the conversion specifier %f." Computing in C 4th Edition.


I am still on chapter 2 and we have not learn about conversion specifiers yet. I think it starts on the next chapter. But below is what I came up with. The only problem is, I did not include the %f in there because I do not know how to use it. I am not sure why the book is wanting us to use something that is taught later on in the chapters. But anyway, another problem I have is, my calculations seems to be off when I checked it with a calculator. Does anyone know whats wrong with the code?

 #include <stdio.h>

int main()
{
       int r, pi;
       
       pi = 3.14159;
       
       

          printf( "Enter the radius of the circle: " );
          scanf( "%d", &r );

         
          printf( "The diameter is %d\n", 2 * r);
          printf( "The circumference is %d\n", pi * 2 * r);
          printf( "The area is %d\n",   pi * r * r );

system ( "pause" );
return 0;
}

[twomers]

Change printf( "The circumference is %d\n", pi * 2 * r);
to printf( "The circumference is %f\n", pi * 2 * r);

Same for the area.

Also, how far off are the calculations? Will you post some examples?

[Nightsky]

Change printf( "The circumference is %d\n", pi * 2 * r);
to printf( "The circumference is %f\n", pi * 2 * r);

Same for the area.

Also, how far off are the calculations? Will you post some examples?

When I changed %d to %f, the values went to zero. Am I suppose to define %f somewhere? I'm not familiar with the %f.


As for the calculations when I had it at %d, it seems like the bigger the radius, the further off the area and circumference. For example, if I entered a radius of 3, it would give me diametere of 6, circumference of 18, and area of 27.

But when I enter 48 as radius, I got diameter of 96, circumference of 288, and area of 6912.

The actual values should be:

Radius: 3 then Diameter: 6, Circumference: 18.85, Area: 28.27

Radius: 48 then Diametere:96, Circumference: 301.59, Area: 7238.23

I assuming it has something to do with the decimals in pi.

[Dave_Sinkula]

You might want to make pi a float, as an int it's 3.

[twomers]

Perhaps you should make pi a float?

ie

int r;
float pi = 3.14.........;

Edit:: Beaten to it

[Nightsky]

I got it. This board is very helpful. I learn so much more here as oppose to in school with the i drink at hooters teacher. lol. Anyway, Thanks!!!