Help on my C programming (noob)

This is the goal:
Prompt the user for the inner and outer diameter and thickness of the washer to be entered in cm. Then prompt for the material density in grams per cubic cm (g/cm^3) and the number of washers in the batch. Finally, print out the expected weight in kg. Make sure that 3 digits after the decimal are always displayed for your results.

When executed, it should say:
Welcome to the Washer Weight Batch Program.
Please enter the following washer information.

Inner diameter in cm: 1.2
Outer diameter in cm: 2.4
Thickness in cm: 0.1
Material density in g/cm^3: 7.87
Quantity in batch: 1000

The expected weight of the washer batch is 2.670 kg.
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Alright. So this is what I have so far. Please let me know what I need to change or add on.

Code:

---

/* Directives */

#include <stdio.h>
#define PI 3.14159

int main(void)
{
float inner, diameter, thickness, density; NOT SURE ON THESE FLOAT VARIABLES

printf("Welcome to the Washer Weight Batch Program.\n");

printf("Please enter the following washer information.\n");

printf("Inner diameter in cm: ");
scanf("%f", &inner); NOT TOO SURE ON THESE EITHER.
printf("Outer diameter in cm: ");
scanf("%f", &diameter);
printf("Thickness in cm: ");
scanf("%f", &thickness);
printf("Material density in g/cm^3: ");
scanf("%f", &density);
printf("Quantity in batch: ");

printf("The expected weight of the washer batch is: %.3f kg.\n");


/* End Program */
return(0);

}

---

It's using the correct equations to make the program calculate the expected weight of the washer batch that is getting me stuck. I'm not 100% sure on computing that.

Well, the math doesn't seem like it's that tough.

First calculate the area of the washer. This is done by: pi*R^2 - pi*r^2. Where R is the outer diameter and r is the inner diameter. Now multiply that by the thickness to get the area. Finally, multiply by the density to get the weight.

UPDATE: I am ALMOST THERE!
When I input(in bold), I don't get the same answer as 2.670 kg. I get 18.096 kg instead.

Inner diameter in cm: 1.2
Outer diameter in cm: 2.4
Thickness in cm: 0.1
Material density in g/cm^3: 7.87
Quantity in batch: 1000

The expected weight of the washer batch is 2.670 kg.

Code:

---

/* homework 6 */

/* Directives */

#include <stdio.h>
#define PI 3.14159

int main(void)
{
float inner, diameter, thickness, density, weight;
int quantity;
printf("Welcome to the Washer Weight Batch Program.\n");

printf("Please enter the following washer information.\n");

printf("Inner diameter in cm: ");
scanf("%e", &inner);
printf("Outer diameter in cm: ");
scanf("%E", &diameter);
printf("Thickness in cm: ");
scanf("%f", &thickness);
weight = PI * pow(diameter,2) - PI * pow(inner,2) * thickness * density;
printf("Material density in g/cm^3: ");
scanf("%f", &density);
printf("Quantity in batch: ");
scanf("%i", &quantity);
printf("The expected weight of the washer batch is: %.3f kg.\n", weight);


/* End Program */
return(0);

}

---

pow() is declared in <math.h>, have you included it?

Quote:

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Originally Posted by BEN10

pow() is declared in <math.h>, have you included it?

---

Yeah, after posting it up, I added the <math.h>

Still not getting the right output. Hmm.

I'm thinking my math equation to find the area of the washer is not right...

Area is PI * r * r not PI * Diameter * Diameter