Thread: Exercise 1 --- Area of a Circle

Write a program that calculates the area of a circle from the radius. The radius will be an integer read in from the keyboard. You will need to use the function pi(). According to my understanding, the functions accept a double argument and returns a double. But I was asked to use the integer for radius, so how do I pass it to the function? Another question is there a function square() because when I inserted a square it was undefined. I have been told that my codes are horrible because of the logic. What does it mean and how do I improve my codes?

Code:

#include<stdio.h>#include<math.h>
#include<stdlib.h>
#define M_PI


double CalcRadius(int x);
int x;
double y;


int main(){


	printf("Enter the radius of the circle\n");
	scanf("%d",&x);
	double CalcRadius(int x);
	printf("The area of the circle is %f\n",y);


	return 0;
}


double CalcRadius(int x)
{
	y= M_PI*x*x;
		return y;
}

For starters, you are not calling the function correctly. I suggest you read up on how to properly call functions.

I think that the radius should be float not just an integer.

I also think that the function to compute area should be CalcArea instead of CalcRadius, because it does not compute radius, but area.

Another think is that you have declared variable y but you have not assigned any value to it.

And colleague Hodor mentioned use of global variables already.

Originally Posted by Hodor

Edit 2: Personal peeve. Do not use the word "codes". The plural of "code" (in the sense you're expressing) is "code".

I'd argue that "code" should actually always be used in the singular (i.e. there can be no plural), since it is considered a mass noun in computer science.

Originally Posted by Matticus

I'd argue that "code" should actually always be used in the singular (i.e. there can be no plural), since it is considered a mass noun in computer science.

Yes, of course it should always be singular. That's what I was saying. But if you refer to a collection of source code, it's not source codes it's still just source code.

There is no debate about this... saying "codes" is like saying "datas".

Oh, I'm not saying "codes" (as a noun) is acceptable in that sense. You just said "the plural of "code"...", and I pointed out how technically it should not be considered plural in the given context.

Looks like PI should be a constant.

Type double or type float really depends on how much precision you want. The difference is really just length - double offers more significant figures.

There is no standard library function called "pi()". Where did you get this exercise from? All I can find is this: "Basic Programming Exercises", and it doesn't indicate any specific languages. While most of the questions appear to be generic enough for most languages, mentioning a specific function like this can be misleading.

When do I use type double or type float?

You should just use doubles, unless you have a specific reason to use floats.

All I can find is this: "Basic Programming Exercises", and it doesn't indicate any specific languages.

Yes, I am trying to do the exercises from that website. So I suppose coding this way, will do?

Code:

#include<stdio.h>#define M_PI 3.14159265358979323846


float square(float x);


main()
{
	float m, area;


	printf("Enter the radius\n");
	scanf("%f", &m);
	area = M_PI * square(m);
	printf("The area of the circle is %f\n", area);
}


float square(float x)
{
	float p;


	p = x*x;
	return(p);
}

set1.1.c(12) : warning C4244: '=' : conversion from 'double' to 'float', possible loss of data

Does this mean I should convert everything into double instead?

Originally Posted by nadeera

Does this mean I should convert everything into double instead?

Yes.

As I said, work with doubles unless you have a specific reason to use floats.

Okay, but as soon as I convert everything it gives me a completely ridiculous answer. Is there anything I missed? Can you try running it, please?

Code:

#include<stdio.h>#define M_PI 3.14159265358979323846
 
double square(double x);
 
main()
{
    double m, area;
 
    printf("Enter the radius\n");
    scanf("%f", &m);
    area = M_PI * square(m);
    printf("The area of the circle is %f\n", area);
}
 
 double square(double x)
{
    double p;
    p = x*x;
    return(p);
}

Did you get warnings when you compiled?

Code:

/*
main.c|10|warning: format '%f' expects type 'float *', but argument 2 has type 'double *'
*/

Code:

scanf("%f", &m);

In "scanf()", use "%lf" for doubles (that's the lower-case letter L).
For "printf()", the "%f" is fine as is.

Did you get warnings when you compiled?

Nope, I did not get any warnings. I changed it as you said, and now it works perfectly. Thank you so much.