Mình làm 2 ngôn ngữ nha
* Pascal :
Program Chu_vi_Dien_tich_hinh_tron;
Uses Crt;
Var r,dt,cv:real;
Begin
    Clrscr;
    Writeln(' Tinh dien tich va chu vi hinh tron:');
    Readln('Tinh dien tich va chu vi hinh tron');
    Write ('Nhap ban kinh r =');
    Readln(r);<br />    dt:=pi*r*r;<br />    cv:=2*pi*r;<br />    
    Writeln('Dien tich hinh tron la:',dt:6:2);
    Writeln('Chu vi hinh tron la:',cv:6:2);
    Readln;
End.

* C : 
#include <stdio.h>
#include <conio.h>
#include <math.h>
#define PI 3.14159
int main() {
            int r;
            float chuvi, dientich;
            printf("Nhap ban kinh r:");
            scanf("%d", &r);
            chuvi = 2*PI*r;
            dientich = PI*r*r;
            printf("Chu vi hinh tron la: %f\n", chuvi);
            printf("Dien tich hinh tron la: %f", dientich);
            getch(); }