Introduction to (Web) Programming

Program 3: conditionals and loops

Due date: Thursday, February 21 at 1:30pm

General instructions


The problems themselves.

  1. Complete the function padEven(s) so that it returns string s if s consists of an even number of characters (i.e., its length is an even number) or returns s with an exclamation point (!) appended
    if the length is odd. Use an if statement without an else. Examples:

     > padEven('Cool')
     "Cool"
     > padEven('Cool!')
     "Cool!!"
  2. Complete threeify(n) so that it returns n divided by 3 if n is divisible by 3 and n times 3 if n is not divisible by 3. You can assume n is a number. Use an if-else statement. Examples:

     > threeify(15)
     5
     > threeify(7)
     21
  3. Complete seasonToNumber(season) so that it returns the number corresponding to the specified string season (1 for Winter, 2 for Spring, etc.). Returns NaN if season is not one of the four seasons. Case insensitive. Use a multiway conditional. Examples:

     > seasonToNumber('winter')
     1
     > seasonToNumber('SPRING')
     2
     > seasonToNumber('Fall')
     4
     > isNaN(seasonToNumber('magicvember'))
     true
  4. Complete middleText so that it returns the string that is in the (lexicographic) middle of the three specified strings s1, s2, and s3. Case sensitive. Examples:

     > middleText('alpha', 'beta', 'gamma')
     "beta"
     > middleText('alpha', 'Beta', 'gamma')
     "alpha"
     > middleText('alpha', 'Beta', 'GAMMA')
     "GAMMA"

    Note: there is nothing particular about this function that makes it work only for strings. (It should work on numbers, too, though I will only test it on strings.)

  5. Complete categorize(m) so that it returns a string of length four categorizing number m. The first character of the returned string indicates whether m is a true number (i.e., not NaN), if so, it is 'y' otherwise 'n'. The second character is either 'n', '+', '0', or '-' where 'n' again indicates NaN, '+' means the number is positive, '-' that it is negative, and '0' that it is zero. The third character is again 'n' if m is NaN, otherwise 'I' for Infinity or 'F' for finite. The final character is 'n' if NaN, '?' if infinite, 'i' if m is a finite integer, or 'f' if m is finite, but not an integer (if it is “fractional”). Use nested ifs. Examples:

     > categorize(4103)
     "y+Fi"
     > categorize(-Infinity)
     "y-I?"
     categorize('hello')
     "nnnn"
     categorize(-3.14)
     "y-Ff"
  6. Complete mask(s) so that it returns a string consisting of the '*' symbol concatenated for the entire length of input string. Use a while loop. Examples:

     > mask('')
     ""
     > mask('hello')
     "*****"
  7. Complete sumSquares(n) so that it returns the sum of the squares of the integers from 1 through n (inclusive). Use a while loop. Example:

     > sumSquares(4)   // 1*1 + 2*2 + 3*3 + 4*4
     30
  8. Complete snakeEyes() so that it repeatedly simulates rolling two six-sided dice until they “land as snake eyes” - meaning the sum of the dice is 2. Return the number of rolls required to arrive at snake eyes. In a comment, explain whether the loop you use is definite or indefinite. Your code should call the function randomRange which has been supplied for you.


    The last two problems involve the factors of positive integers. Recall that m is a factor of n if m divides into n without any remainder. For example, the factors of 36 are: 1, 2, 3, 4, 6, 9, 12, 18 and 36 itself. We say that factors of a number that are neither 1 nor the number itself are nontrivial factors. A number is perfect if it is the sum of all its factors other than itself. (Perfect numbers are quite fascinating!)

    We can easily test if a number d is a factor of a number q by using the remainder operator and comparing the result to zero:

      > 36 % 12 === 0   // 12 is a factor of 36
      true
      > 36 % 11 === 0   // 11 is not a factor of 36
      false
  9. Complete isPerfect(n) so that it returns true if n is a perfect number and returns false otherwise. Examples:

     > isPerfect(6)   // 6 = 1 + 2 + 3
     true
     > isPerfect(15)  // 15's factors are 1, 3, and 5
     false
  10. (Challenging.) Complete factors(start, stop) so that it returns a string representation of all the nontrivial factors of each number between start (inclusive) and stop (exclusive). Use nested while loops. The string should consist of one line for each number from start to stop. Each line should consist of the number whose factors are being presented, followed by a colon, followed by all its notrivial factors with two spaces between each factor. Example:

    > console.log(factors(10, 15))
    10: 2  5
    11:
    12: 2  3  4  6
    13:
    14: 2  7

Challenge problems


Restrictions and requirements

All of your functions should return a value. Make sure that your functions have a single return statement as the last statement within the body of the function. Keep the return simple: just return a variable.

Your code should not use prompt, confirm or alert.

For numbers, you can use the standard five arithmetic operations:

+   -   *   /   %

the six arithmetic comparison operations:

===   !==   <   >   <=   >=

and isNan and isFinite. (randomRange uses Math.floor and Math.random but you should not need either.)

For Booleans you can use the literals true and false and the three standard Boolean operators:

!   &&   ||

For strings, you can use:

===   !==   <   >   <=   >=   .length   .toLowerCase   .toUpperCase

You should not need the typeof operator (except, possibly, for the categorize problem).

Remember, \n is the character than when displayed (either using alert or console.log) indicates that the next characters should appear on a new line.

You may use the short hand modifiers for assignments:

x++;      // shorthand for x = x + 1;
x--;      // shorthand for x = x - 1;
x += y;   // shorthand for x = x + y; (works for strings, too)
x -= y;   // shorthand for x = x - y;
x *= y;   // shorthand for x = x * y;

To experiment more directly with my solutions, you can open up on a console while viewing this page and try examples such as:

 > padEven('hello')
 "hello!"
 > sumSquares(4)
 30