ITFN 2313 Mid-Term Practice (Fall 2009)

1. Write a recursive function that displays the numbers counting up by 2 (0, 2, 4, 6, …) to 100. Be sure you indicate how it would be invoked to get the desired results. [15 Points]

static void RecursiveFunction(int x)

{

if (x > 100) //Condition to stop recursion

return; //Exit out of function

else

{

Console.WriteLine(x);

RecursiveFunction(x + 2); //Call myself

}

}

static void Main(string[] args)

{

RecursiveFunction(0);

Console.Read();

}

2. Write a snippet of code that asks the user to enter a number. Then, create an exception handler that responds if the user enters something other than a number. Hint: Your answer should include a try block and a catch block. (15 Points)

static void Main(string[] args)

{

int num;

Console.WriteLine("Enter a number");

try

{

num = Convert.ToInt32(Console.ReadLine());

}

catch (FormatException)

{

Console.WriteLine("That is not a number!");

}

}

3. What is the output of the following code assuming it is called as f(1)?

11, 9, 7, 5, 3, 1

{static void f(int i)

{

if (i < 10)

f(i+2);

Console.WriteLine(i);

}

4. Write a recursive function that displays the numbers counting up by 3 (0, 3, 6, 9, …) to 99.
   static void RecursiveFunction(int x)

{

if (x > 99) //Condition to stop recursion

return; //Exit out of function

else

{

Console.WriteLine(x);

RecursiveFunction(x + 3); //Call myself

}

}

static void Main(string[] args)

{

RecursiveFunction(0);

Console.Read();

}

5. Write a recursive function that takes in as a parameter N, a number (int), and prints out the numbers from N down to 1 (inclusively) in descending order and then in ascending order. You must use recursion in your solution. [15 Points] Here is the function header:

void Print_N_to_1_to_N(int n)

For example, Print_N_to_1_to_N(6)would print 6 5 4 3 2 1 2 3 4 5 6.

public static void Print_N_to_1_to_N(int n)

{

if (n > 0)

{

Console.Write(n);

Print_N_to_1_to_N(n - 1);

Console.Write(n);

}

}

6. The following lines of code will throw what exception? What is the throw point? Write a try/catch to handle this exception. [15 Points]

int numOne = 4;
int numTwo = 0;

int sum=(numOne/numTwo); Throw point – DivideByZero exception

try

{

int sum = (numOne / numTwo);

}

catch (DivideByZeroException)

{

Console.WriteLine("You cannot divide by zero");

}

7. Write a recursive function that takes in as a parameter N, a number (int), and returns the sum of the numbers from 1 to N (inclusively). You must use recursion in your solution. [15 Points] Here is the function header:

int Sum_1_to_N(int n)

For example, Sum_N_to_1(5)would be 15 (1 + 2 + 3 + 4 + 5).

public static int Sum1_to_n(int n)

{

int answer = n;

if (n > 0)

{

answer = n + (Sum1_to_n(n - 1));

}

return answer;

}

8. What does the following code accomplish if is called as follows: testString(s, 0, s.length-1)? Briefly explain what happens with each line. [15 Points]

PALINDROME TEST

public static bool testString(string s, int left, int right) function that takes in a string and two ints. The two ints represent the start of the string and the end of the string

{

if (left >= right) terminating condition tests # of first letter against # of last letter

return true; e.g. if string is “Sandra” left = 0 and right is = 5; makes progress toward middle of string

else if (s[left] != s[right]) terminating condition tests if first letter is not equal to last letter

return false;

else

return TestString(s, left + 1, right -1); recursive call, increases left by one, reduces right by one.

}