program using area() and perimeter() function

[forget you]

it says declaration error in this program ,what is that
and please help me

#include<stdio.h>
#include<conio.h>
# define pi=22/7
void area();
void perimeter();
void main()
{
area();
perimeter();
getch();
}
void area()
void perimeter()
{
float r,pi,A,P;
clrscr();
printf("enter the radius :\n");
scanf("%d",&r);
A=pi*r*r;
P=2*pi*r;
printf("the area and perimeter are %f and %f",A,P);
}

[Rabbit]

Please use code tags when posting code.

On line 12, you never finish the area function and jump right into the perimiter function.

[divideby0]

scanf("%d",&r);
 

this is the wrong format specifier; for floats, use "%f"

#define PI 22/7
 

I'd think you'd be getting integer division here. Promote it to a float using 22/7.0 or such

you haven't coded the function definition for area(), but tried to declare its prototype twice.

void area(void); // function prototype
 
int main()
{
   area(); // function call
   ...
}
 
void area(void) // function definition
{
   // area's definition
}

[donbock]

I notice you're using float type. Most folks use double.

A better rational approximation of pi is 355/113.
22/7: error = 1.26E-03
355/113: error = 2.67E-07
Look here and here for more about approximations of pi.

Suggested C code.
Notice the constants are double's. There is no point to using float constants because the division will promote them to double's any way.

#define PI (355./113.)