CS 131 PROGRAMMING ASSIGNMENT 4

    Problem 26, p. 124. Calculate the maximum heart rate and percentages for 5 people, 
    outputting the target zone for each. Print the average maximum heart rate at the end.

  * Select reasonable ranges for age and pulse and incorporate error checking into 
    your program. At the end, print the average maximum heart rate of the valid inputs 
    and the number of invalid inputs.