Problems

1. write a program that reads in the radius and computes the area of a circle;
2. extend the program to test whether the area is negative; if so just STOP. This introduces IF blocks, and logical expressions;
3. extend the program to read 5 radii; this introduces a DO loop and integer variables; CYCLE and EXIT.
4. extend the code to first read all 5 radii and then compute all 5 areas; this introduces arrays. The dimension (N=5) is a PARAMETER.