**C program for area of circle**

#include <stdio.h>

#define PI 3.141

int main(){

float r, a;

printf("Radius: ");

scanf("%f", &r);

a = PI * r * r;

printf("%f\n", a);

return 0;

}

**Mathematical formula for area of circle:**

Here
Pie is constant which is equal to

Pie = 22/7 or
3.14159265358979323846264338327950288419716939937510...

Radius
is radius of the circle.

7. Write a c program to find the area of rhombus.

8. Write a c program to find the area of parallelogram.