Summer exercises

//1
A)
|                        | num | output |
|------------------------+-----+--------|
|                        |  10 |        |
|------------------------+-----+--------|
| if (num<20)            |     |        |
| while (num>2)          |     |        |
| num -=2;               |   8 |        |
|------------------------+-----+--------|
| while (num>2)          |     |        |
| num -=2;               |   6 |        |
|------------------------+-----+--------|
| while (num>2)          |     |        |
| num -=2;               |   4 |        |
|------------------------+-----+--------|
| while (num>2)          |     |        |
| num -=2;               |   2 |        |
|------------------------+-----+--------|
| if (num==2 || num==40) |     |        |
| return 1;              |     |      1 |
|------------------------+-----+--------|
| return 0;              |     |        |
|------------------------+-----+--------|

B)
|                        | num | output |
|------------------------+-----+--------|
|                        |  33 |        |
|------------------------+-----+--------|
| else                   |     |        |
| while (num<40)         |     |        |
| num+=2;                |  35 |        |
|------------------------+-----+--------|
| while (num<40)         |     |        |
| num+=2;                |  37 |        |
|------------------------+-----+--------|
| while (num<40)         |     |        |
| num+=2;                |  39 |        |
|------------------------+-----+--------|
| while (num<40)         |     |        |
| num+=2;                |  41 |        |
|------------------------+-----+--------|
| if (num==2 || num==40) |     |        |
| return 1;              |     |        |
|------------------------+-----+--------|
| return 0;              |     |      0 |
|------------------------+-----+--------|

//2
static void Swap(string a)
        {
            if (a.Length > 100)
            {
                Console.WriteLine("String length too long (100 characters max!)");
            }
            else
            {
                if (a.Length % 2 == 1)
                {
                    char last = a[a.Length - 1], first = a[0];
                    string new_string = last + a.Substring(1, a.Length - 2) + first;
                    Console.WriteLine(new_string);
                }
                else
                {
                    char last = a[a.Length / 2], first = a[a.Length / 2 - 1];
                    string new_string = a.Substring(0, a.Length / 2 - 1) + last + first + a.Substring(a.Length / 2 + 1);
                    Console.WriteLine(new_string);
                }
            }
        }

//3 assuming the array is already defined and is named "a"
            int max = 0, index = 0;
            for(int i = 0; i < a.Length; i++)
            {
                if(a[i] > max) {
                    max = a[i];
                    index = i;
                }
            }
            a[index] = a[a.Length - 1];
            a[a.Length - 1] = max;

//4 assuming the array is already defined as is named "a"
            bool last = false;                                   // true if the last character was a letter
            for (int i = 0; i < a.Length; i++)
            {
                bool current = false;                           // true if this character is a letter
                for (char letter = 'a'; letter <= 'z'; letter++)
                    if (!current)
                        if (letter == a[i])
                            current = true;
                if (current == false && last == true)
                {
                    Console.Write("{0} ", i - 1);
                }
                last = current;
            }

//5
A )
|                                   | A                  | T     | i | x | n | output |
|-----------------------------------+--------------------+-------+---+---+---+--------|
|                                   | [1, 2, 3, 4, 5, 6] | true  |   |   | 6 |        |
|-----------------------------------+--------------------+-------+---+---+---+--------|
| for (int i = 0; i <= n - 2; i++): |                    |       | 0 |   |   |        |
| int x = A[i];                     |                    |       |   | 1 |   |        |
| if (i != A[x]):                   |                    |       |   |   |   |        |
| T = false;                        |                    | false |   |   |   |        |
|-----------------------------------+--------------------+-------+---+---+---+--------|
| for (int i = 0; i <= n - 2; i++): |                    |       | 1 |   |   |        |
| int x = A[i];                     |                    |       |   | 2 |   |        |
| if (i != A[x]):                   |                    |       |   |   |   |        |
| T = false;                        |                    | false |   |   |   |        |
|-----------------------------------+--------------------+-------+---+---+---+--------|
| for (int i = 0; i <= n - 2; i++): |                    |       | 2 |   |   |        |
| int x = A[i];                     |                    |       |   | 3 |   |        |
| if (i != A[x]):                   |                    |       |   |   |   |        |
| T = false;                        |                    | false |   |   |   |        |
|-----------------------------------+--------------------+-------+---+---+---+--------|
| for (int i = 0; i <= n - 2; i++): |                    |       | 3 |   |   |        |
| int x = A[i];                     |                    |       |   | 4 |   |        |
| if (i != A[x]):                   |                    |       |   |   |   |        |
| T = false;                        |                    | false |   |   |   |        |
|-----------------------------------+--------------------+-------+---+---+---+--------|
| Console.WriteLine(T)              |                    |       |   |   |   | false  |

B) [4, 5, 3, 2, 0, 0]


//6
            int[] teachers = new int[100];
            for (int i = 0; i < teachers.Length; i++)
                teachers[i] = 0;
            for (int i = 0; i < 900; i++)
            {
                Console.WriteLine("Please enter your two favorite teachers:");
                int first = int.Parse(Console.ReadLine()) - 1, second = int.Parse(Console.ReadLine()) - 1;
                while (second == first)
                {
                    Console.WriteLine("Your can't pick the same number twice! please try again:");
                    second = int.Parse(Console.ReadLine()) - 1;
                }
                teachers[first] += 1;
                teachers[second] += 1;
            }
            int max = 0, after_max = 0, index = 0;
            Console.WriteLine("Teachers that aren't liked at all:");
            for (int i = 0; i < teachers.Length; i++)
                if (teachers[i] == 0)
                    Console.Write("{0} ", i + 1);
            Console.WriteLine();
            Console.WriteLine("The teacher that is liked the most:");
            for (int i = 0; i < teachers.Length; i++)
            {
                if (teachers[i] > max)
                {
                    index = i + 1;
                    max = teachers[i];
                }
            }
            Console.WriteLine(index);
            Console.WriteLine("The teacher is the second most liked:");
            for (int i = 0; i < teachers.Length; i++)
            {
                if (teachers[i] > after_max && teachers[i] < max)
                {
                    index = i + 1;
                    max = teachers[i];
                }
            }
            Console.WriteLine(index);

//7
        static void Check(string[] a)
        {
            bool symmetrical = true;
            char last = a[0][a[0].Length - 1];
            for (int i = 1; i < a.Length; i++)
            {
                if (symmetrical)
                {
                    if (a[i][0] != last)
                    {
                        symmetrical = false;
                    }
                    else
                        last = a[i][a[i].Length - 1];
                }
            }
            if (symmetrical)
                Console.WriteLine("The array is symmetical!");
            else
                Console.WriteLine("The array is not symmetrical!");
        }

//8
        static int Test8(int[] a, int k)
        {
            int sum = 0;
            for (int i = k; i < a.Length; i++)
                sum += a[i];
            return sum;
        }
        static void Main(string[] args)
        {
            int[] a = { 10, 5, 8, 7, 3 }; // just as an example
            int n = a.Length;
            int[] b = new int[n];
            for (int i = 0; i < b.Length; i++)
                b[i] = Test8(a, i);
        }

//9
        static bool Tri(string s)
        {
            if (s.Length != 15)
                return false;
            char[] chars = s.Substring(5, 5).ToCharArray();
            Array.Reverse(chars);
            string middle = new string(chars);
            if (s.Substring(10, 5) == middle && s.Substring(0, 5) == middle)
                return true;
            return false;
        }
        static void Main(string[] args)
        {
            string[] a = new string[10];
            int sum = 0;
            for (int i = 0; i< a.Length; i++)
            {
                a[i] = Console.ReadLine();
                if (Tri(a[i]))
                    sum++;
            }
            //sum will be the ammount of mahrozot meshulashot
//10
        static int DaysPassed(int[] year, int day, int month)
        {
            int daysPassed = 0;
            for (int i = 0; i < month - 1; i++)
                daysPassed += year[i];
            return daysPassed + day;
        }
        static void Main(string[] args)
        {
            int[] year = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
            int day = int.Parse(Console.ReadLine()), month = int.Parse(Console.ReadLine());
            while (day != 0 && month != 0)
            {
                if (DaysPassed(year, day, month) > 60)
                    Console.WriteLine("The date is too far.");
                else if (DaysPassed(year, day, month) < 10)
                    Console.WriteLine("The date is too close.");
                else
                    Console.WriteLine("The date is good.");
                day = int.Parse(Console.ReadLine());
                month = int.Parse(Console.ReadLine());
            }
        }