01 #include<stdio.h>

02 #include<math.h>

03

04 int main()

05 {

06 int side;

07 float area;

08

09 printf("nEnter the Length of the Side : ");

10 scanf("%d", &side);

11

12 area = 2*(1+sqrt(2))*side*side;

13

14 printf("nArea of Regular Octagon : %.2f", area);

15 return 0;

16 }

OUTPUT :

Enter the Length of Side : 3

Area of Regular Octagon : 43.46