Write a C$++$ program $]$Examples

a$)$ Write a program to compute the area of a circle of radius $r.$

$A=r^2$

b$)$ Write a program to compute the volume of a sphere.

$V=\frac{4}{3}r$

c$)$ Write a program to compute the tension in a cord given the following values:

$m1=100,m2=50,g=9\mathrm{.}81$

$T=\frac{2m_1{m}_2}{m_1+m_2}g$