5 files changed, 249 insertions, 0 deletions
diff --git a/Sem. 04/example01_no_functions.cpp b/Sem. 04/example01_no_functions.cpp
new file mode 100644
index 0000000..06e6629
--- /dev/null
+++ b/Sem. 04/example01_no_functions.cpp
@@ -0,0 +1,39 @@
+#include <iostream>
+using namespace std;
+
+
+int main()
+{
+	int n;
+	cin >> n;
+	
+	for (int i = 6; i < n; i += 6)
+	{
+		int firstToCheck = i - 1;
+		int secondToCheck = i + 1;
+
+		//prime check
+		bool isFirstPrime = true;
+		double temp = sqrt(firstToCheck);
+		for (int j = 2; j <= temp; j++)
+		{
+			if (firstToCheck % j == 0)
+				isFirstPrime = false;
+		}
+
+		if (!isFirstPrime)
+			continue;
+
+		//prime check
+		bool isSecondPrime = true;
+		double temp2 = sqrt(secondToCheck);
+		for (int j = 2; j <= temp2; j++)
+		{
+			if (secondToCheck % j == 0)
+				isSecondPrime = false;
+		}
+
+		if (isSecondPrime)
+			cout << firstToCheck << " " << secondToCheck << endl;
+	}
+}
+\ No newline at end of file
diff --git a/Sem. 04/example01_with_functions.cpp b/Sem. 04/example01_with_functions.cpp
new file mode 100644
index 0000000..f33b6b9
--- /dev/null
+++ b/Sem. 04/example01_with_functions.cpp
@@ -0,0 +1,27 @@
+#include <iostream>
+using namespace std;
+
+bool isPrime(int n)
+{
+	double temp = sqrt(n);
+
+	for (int i = 2; i <= temp; i++)
+	{
+		if (n % i == 0)
+			return false;
+	}
+
+	return true;
+}
+
+int main()
+{
+	int n;
+	cin >> n;
+
+	for (int i = 6; i < n; i += 6)
+	{
+		if (isPrime(i - 1) && isPrime(i + 1))
+			cout << i - 1 << " " << i + 1 << endl;
+	}
+}
+\ No newline at end of file
diff --git a/Sem. 04/example02-08.cpp b/Sem. 04/example02-08.cpp
new file mode 100644
index 0000000..002a8ab
--- /dev/null
+++ b/Sem. 04/example02-08.cpp
@@ -0,0 +1,141 @@
+#include <iostream>
+using namespace std;
+
+
+//задача 2:
+// Напишете функция, която приема цяло число и връща обърнатото му.
+// 1234 - 4321
+
+int reverse(unsigned int n)
+{
+	unsigned int result = 0;
+
+	while (n != 0)
+	{
+		int lastDigit = n % 10;
+		(result *= 10) += lastDigit;
+		n /= 10;
+	}
+
+	return result;
+}
+
+//задача 3: Напишете функция, която приема цяло число и връща дали е палиндром
+
+//12321 -> true
+//123 -> false;
+
+bool isPalindrome(unsigned int n)
+{
+	return n == reverse(n);
+}  
+//задача 4: Напишете функция, която приема две цели числа - n и k.
+//Функцията да връща дали k е суфикс на n.
+// n = 1234 k = 34 true
+// n = 1234 k = 234 true
+// n = 1234 k = 1234 true
+// n = 1234 k = 23 false
+
+bool isSuffix(unsigned int n, unsigned int k)
+{
+	if (k == 0 && (n % 10 != 0))
+		return false;
+
+	while (k != 0)
+	{
+		int lastDigitOfN = n % 10;
+		int lastDigitOfK = k % 10;
+
+		if (lastDigitOfN != lastDigitOfK)
+			return false;
+
+		n /= 10;
+		k /= 10;
+	}
+
+	return true;
+}
+
+
+// задача 5: Напишете функция, която приема две цели числа -n и k.
+// Функцията да връща дали k е префикс на n.
+
+// n = 1234, k = 12  true
+// n = 1234, k = 23 false;
+
+// u е префикс на w  <-> u ^rev е суфикс на w^rev
+bool isPrefix(unsigned int n, unsigned  int k)
+{
+	return isSuffix(reverse(n), reverse(k));
+}
+
+// задача 6: Напишете функция, която приема две числа - n,k.
+// Функцията връща дали k е инфикс на n.
+
+bool isInfix(unsigned int n, unsigned int k)
+{
+	if (n == 0 && k == 0)
+		return true;
+
+	while (n > 0)
+	{
+		if (isSuffix(n, k))
+			return true;
+		n /= 10;
+	}
+	return false;
+}
+
+
+//задача.
+//Да се напише функция, която приема цяло число и връща дали цифрите му са сортирани.
+
+// 1234 true
+// 12379 true
+// 1231 false
+// 4321 true
+// 4325 false
+// 1111 true
+
+bool areDigitsSortedAscending(unsigned int n)
+{
+	while (n >= 10)
+	{
+		int lastDigit = n % 10;
+		int prevLastDigit = (n / 10) % 10;
+
+		if (prevLastDigit > lastDigit)
+			return false;
+
+		n /= 10;
+	}
+
+	return true;
+}
+
+bool areDigitsSortedDescending(int n)
+{
+	return areDigitsSortedAscending(reverse(n));
+}
+
+bool areDigitsSorted(int n)
+{
+	return areDigitsSortedDescending(n) || areDigitsSortedAscending(n);
+}
+
+//задача.
+// Напишете функция, която приема цяло число и връща дали се съдържа само от еднакви цифри.
+
+//Вход: 11111 Изход:true
+//Вход: 123 Изход: false
+
+bool containOnlyOneDigit(int n)
+{
+	return areDigitsSortedDescending(n) && areDigitsSortedAscending(n);
+}
+
+
+int main()
+{
+	cout << containOnlyOneDigit(444) << endl;
+}
+\ No newline at end of file
diff --git a/Sem. 04/example09 .cpp b/Sem. 04/example09 .cpp
new file mode 100644
index 0000000..f7f072b
--- /dev/null
+++ b/Sem. 04/example09 .cpp
@@ -0,0 +1,21 @@
+#include <iostream>
+using namespace std;
+
+unsigned int log(unsigned int n, unsigned int k)
+{
+	int count = 0;
+
+	while (n >= k)
+	{
+		n /= k;
+		count++;
+	}
+
+	return count;
+}
+
+
+int main()
+{
+	cout << log(4, 10) << endl;
+}
+\ No newline at end of file
diff --git a/Sem. 04/example10.cpp b/Sem. 04/example10.cpp
new file mode 100644
index 0000000..f7f072b
--- /dev/null
+++ b/Sem. 04/example10.cpp
@@ -0,0 +1,21 @@
+#include <iostream>
+using namespace std;
+
+unsigned int log(unsigned int n, unsigned int k)
+{
+	int count = 0;
+
+	while (n >= k)
+	{
+		n /= k;
+		count++;
+	}
+
+	return count;
+}
+
+
+int main()
+{
+	cout << log(4, 10) << endl;
+}
+\ No newline at end of file