Exercise 5 draft

Added Exercise 5 but incomplete

Informatik_I/Exercise_5/Task_1/calendar.cpp

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+#include "calendar.h"
+#include <string>
+
+// PRE: a year greater or equal than 1900
+// POST: returns whether that year was a leap year
+bool is_leap_year(int year) {
+  if (year >= 1900) {
+    if (year % 4 == 0 && year % 100 != 0)
+      return true;
+    else if (year % 4 == 0 && year % 400 == 0)
+      return true;
+  }
+  return false;
+}
+
+// PRE: a year greater or equal than 1900
+// POST: returns the number of days in that year
+int count_days_in_year(int year) {
+  if (year >= 1900) {
+    if (is_leap_year(year) == true)
+      return 366;
+    return 365;
+  }
+  return 0;
+}
+
+// PRE: a month between 1 and 12 and a year greater or equal than 1900
+// POST: returns the number of days in the month of that year
+int count_days_in_month(int month, int year) {
+  if (year >= 1900 && month > 0 && month <= 12) {
+    if (is_leap_year(year) == false) {
+      if (month % 2 != 0 && month != 2 && month <= 7)
+        return 31;
+      else if (month % 2 == 0 && month != 2 && month > 7)
+        return 31;
+      else if (month == 2)
+        return 28;
+      else
+        return 30;
+    } else {
+      if (month % 2 == 0 && month != 2 && month <= 7)
+        return 31;
+      else if (month % 2 == 0 && month != 2 && month > 7)
+        return 31;
+      else if (month == 2)
+        return 29;
+      else
+        return 30;
+    }
+  }
+  return 0;
+}
+
+// PRE:  n/a
+// POST: returns whether the given values represent a valid date
+bool is_valid_date(int day, int month, int year) {
+  if (day > 0 && day <= count_days_in_month(month, year) && month > 0 &&
+      month <= 12 && year >= 1900)
+    return true;
+  return false;
+}
+
+// PRE: the given values represent a valid date
+// POST: returns the number of days between January 1, 1900 and this date
+// (excluding this date)
+int count_days(int day, int month, int year) {
+  int res_day = 0;
+  if (is_valid_date(day, month, year) == true) {
+    for (int j = 1901; j <= year; ++j) {
+      res_day += count_days_in_year(j);
+    }
+    for (int j = 1; j < month; ++j) {
+      res_day += count_days_in_month(j, year);
+    }
+    res_day += (day - 1);
+  }
+  return res_day;
+}
+
+// PRE: the given values represent a (potentially invalid) date
+// POST: prints the weekday if the date is valid or "invalid date" otherwise.
+//      Everything must be printed in lowercase.
+void print_weekday(int day, int month, int year) {
+  if (is_valid_date(day, month, year) == true) {
+    std::string days[7] = {"sunday",   "monday", "tuesday", "wednesday",
+                           "thursday", "friday", "saturday"};
+    std::cout << days[((count_days(day, month, year) + 1) % 7)];
+  } else
+    std::cout << "invalid date";
+}

Informatik_I/Exercise_5/Task_2/functions.cpp

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+// PRE:  x > 0
+// POST: returns n^x
+int f1(int n, int x) {
+  int res = 1;
+  for (; x > 0; x--) {
+    res *= n;
+  }
+  return res;
+}
+
+// PRE:  n > 0
+// POST: returns number of devisions by 10 with n
+int f2(int n) {
+  int i = 0;
+  while (n > 0) {
+    n = n / 10;
+    ++i;
+  }
+  return i;
+}
+
+// PRE:  n > 1
+// POST: returns a bool to determine if n is prime
+bool f3(int n) {
+  int i = 2;
+  for (; n % i != 0; ++i);
+  return n == i;
+}
+
+// PRE:  n is square number
+// POST: returns root of n
+int f4(int n) {
+  int i = 0;
+  while (i * i != n) {
+    ++i;
+  }
+  return i;
+}

Informatik_I/Exercise_5/Task_3/main.md

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+Please write your solution here.
+For your convenience we have added a template for your answers below.
+
+Note: Remember to also describe the problem of the function.
+
+# Function `c++|is_even`:
+
+The problem with this function is that it does not return a bool if the number `i` is uneven.
+
+```c++
+// PRE:  n/a
+// POST: returns true if i is even. If not it returns false.
+bool is_even(int i) {
+  if (i % 2 == 0) return true;
+  else return false;
+}
+```
+
+# Function `c++|invert`:
+
+The problem with this function is
+
+```c++
+// PRE: x is positive or negative but not zero.
+// POST: returns inverse with respect to multiplication of x.
+double invert(int x) {
+  // TODO: Fix code below.
+  if (x != 0) {
+      return 1.0 / x;
+  }
+  else
+    std::cout << "0 has no inverse!";
+}
+```
+

Informatik_I/Exercise_5/Task_4/run_length.cpp

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+#include "run_length.h"
+
+void encode() {
+  int i;
+  int c;
+  int count;
+  std::cin >> i;
+  std::cout << 1 << " ";
+  while (i != -1) {
+    count = 0;
+    c = i;
+    while (i == c && i >= 0 && i <= 255) {
+      ++count;
+      std::cin >> i;
+      if (count == 255) {
+        break;
+      }
+    }
+    if (i < -1 || i > 255) {
+      if (count == 0) {
+        std::cout << "error";
+        return;
+      } else {
+        std::cout << count << " ";
+        std::cout << c << " ";
+        std::cout << "error";
+        return;
+      }
+    }
+    std::cout << count << " ";
+    std::cout << c << " ";
+  }
+  std::cout << -1;
+}
+
+void decode() {
+  int i;
+  int count;
+  std::cin >> count;
+  std::cin >> i;
+  std::cout << 0 << " ";
+  while (count != -1) {
+    if (i < -1 || i > 255) {
+      std::cout << "error";
+      return;
+    }
+    if (count < -1 || count > 255) {
+      std::cout << "error";
+      return;
+    }
+    for (int j = 0; j < count; ++j) {
+      std::cout << i << " ";
+    }
+    std::cin >> count;
+    if (count != -1)
+      std::cin >> i;
+    if (i == -1) {
+      std::cout << "error";
+      return;
+    }
+  }
+  std::cout << -1;
+}