area of circle using functions

#include<conio.h>
#include<stdio.h>
void main()
{
float area(float);
float r,z;
clrscr();
printf("enter the radius");
scanf("%f",&r);
z=area(r);
printf("area is %f",z);
getch();
}
float area(float a)
{
float f;
f=3.14*a*a;
return f;
}