diff --git a/.gitignore b/.gitignore
index 87f6767..88d050b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1 @@
-main*
\ No newline at end of file
+main
\ No newline at end of file
diff --git a/Cviko4_1/main.c b/Cviko4_1/main.c
new file mode 100644
index 0000000..71790a0
--- /dev/null
+++ b/Cviko4_1/main.c
@@ -0,0 +1,75 @@
+#include "types.h"
+#include <stdio.h>
+
+/**
+ * Determine whether the provided character is alphabetic.
+ *
+ * @param c character
+ *
+ * @return true when the provided character `c` is alphabetic;
+ *    false otherwise
+ */
+bool is_alpha(char c) {
+  // TODO: 1. Check whether the value in c represents an alphabetic ASCII
+  // character
+  return ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'));
+}
+
+/**
+ * Determine whether all characters of the provided `string`
+ *    (character array) are alphabetic.
+ *
+ * @param string input string
+ *
+ * @return true when all characters in the provided string are alphabetic;
+ * 	  false otherwise
+ */
+bool is_name(char string[]) {
+  // TODO: 1. For each character in string
+  //   - determine whether it is alphabetic by calling is_aplha function
+  bool is = true;
+  int i = 0;
+  while (true) {
+    if (string[i] == '\0') {
+      break;
+    }
+    if (!is_alpha(string[i])) {
+      is = false;
+      break;
+    }
+    ++i;
+  }
+  return is;
+}
+
+#ifndef TEST_BUILD
+
+int main() {
+  // Limit the size of names to 20 characters + terminating '\0'
+  char name[21];
+  char surname[21];
+
+  // Let the user specify their name
+  printf("Please provide your name: ");
+  scanf("%20s", name);
+
+  // Call our new function that checks if the name contains only alphabetic
+  // symbols The argument supplied to the function can have a different name
+  // than the one specified in the function definition.
+  if (!is_name(name)) {
+    printf("Provided name contains non-alphabetic characters!\n");
+    return 1;
+  }
+
+  printf("Please provide your surname: ");
+  scanf("%20s", surname);
+  if (!is_name(surname)) {
+    printf("Provided surname contains non-alphabetic characters!\n");
+    return 1;
+  }
+
+  printf("Your full name is: %s %s\n", name, surname);
+  return 0;
+}
+
+#endif
diff --git a/Cviko4_2/main.c b/Cviko4_2/main.c
new file mode 100644
index 0000000..caab9ba
--- /dev/null
+++ b/Cviko4_2/main.c
@@ -0,0 +1,129 @@
+#include "types.h"
+#include <limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+/**
+ * Get the largest value in the provided array
+ *
+ * @note We assume the array is not empty!
+ *
+ * @param array Source integer array
+ * @param length Size of the array
+ *
+ * @return the largest value in the provided array
+ */
+int get_max(int array[], int length) {
+  // TODO: 1. Find the largest value in the array
+  //   be mindful of possible array values
+  //   (eg. they may all be negative or extremely large)
+  int result = INT_MIN;
+  for (int i = 0; i < length; ++i) {
+    if (array[i] > result) {
+      result = array[i];
+    }
+  }
+
+  // TODO: 2. Return the value found
+  return result;
+}
+
+/**
+ * Get the sum of all values in the provided array
+ *
+ * @param array Source integer array
+ * @param length Size of the array
+ *
+ * @return sum of all values in the array
+ */
+int get_sum(int array[], int length) {
+  // TODO: 1. Sum up all the values of the array
+  int result = 0;
+  for (int i = 0; i < length; ++i) {
+    result += array[i];
+  }
+  // TODO: 2. Return the value
+  return result;
+}
+
+/**
+ * Check that for all indices (plural of index),
+ *   array1 has smaller values than array2
+ *
+ * @example
+ * arr1: [2, 4, 1, 10, -5]
+ * arr2: [8, 9, 2, 99, -1]
+ *        ^  ^  ^  ^^  ^^
+ *
+ * @example
+ * arr1: [2, 4, 9, 10, -5]
+ * arr2: [8, 9, 2, 99, -1]
+ *        ^  ^  x
+ *
+ * @note We assume the arrays are of the same length!
+ *
+ * @param array1 First integer array
+ * @param array2 Second integer array
+ * @param array_length Length of both arrays
+ *
+ * @return true when all values at all indices of array1 are
+ *    smaller than corresponding values from array2;
+ *    false otherwise
+ */
+bool values_are_smaller_than(int array1[], int array2[], int array_length) {
+  // TODO: 1. Iterate over all the array items and compare
+  //   values from array1 with corresponding ones in array2
+  bool result = true;
+  for (int i = 0; i < array_length; ++i) {
+    if(array1[i] >= array2[i]){
+        result = false;
+        break;
+    }
+  }
+
+  // TODO: 2. Return false when there is value in array1
+  //    larger than corresponding one in array2
+
+  // TODO: 3. Return true when all the items have been checked
+
+  return result;
+}
+
+#ifndef TEST_BUILD
+
+int main() {
+  int arr1[5];
+
+  printf("Please select five numbers: ");
+  for (int index = 0; index < 5; index++) {
+    scanf("%d", &arr1[index]);
+  }
+
+  // We can either save the maximum value into our new variable and then use it
+  // later
+  int arr_max = get_max(arr1, 5);
+  printf("Maximum array value: %d\n", arr_max);
+
+  // Or we can use the function call directly = function call is an expression!
+  printf("Sum of array values: %d\n", get_sum(arr1, 5));
+
+  // Read another five numbers so that we can test the smaller_than function
+  int arr2[5];
+  printf("Please select another five numbers: ");
+  for (int index = 0; index < 5; index++) {
+    scanf("%d", &arr2[index]);
+  }
+
+  // We do not actually have to use the return value
+  // We have seen this before with functions such as printf and scanf
+  // - they also have a return value!
+  if (values_are_smaller_than(arr1, arr2, 5)) {
+    printf("The first array is smaller than the second.\n");
+  } else {
+    printf("The first array is not smaller than the second.\n");
+  }
+
+  return 0;
+}
+
+#endif
diff --git a/Cviko4_3/main.c b/Cviko4_3/main.c
new file mode 100644
index 0000000..b46eaef
--- /dev/null
+++ b/Cviko4_3/main.c
@@ -0,0 +1,207 @@
+#include "types.h"
+#include <limits.h>
+#include <stdio.h>
+
+/**
+ * Check if the value is in the supplied set
+ *
+ * @param set Integer array representing a set
+ * @param length Length of the provided array
+ * @param value Value to be looked up in the set
+ *
+ * @return true when the provided `value` is in `set`;
+ *    false otherwise
+ */
+bool is_in_set(int set[], int length, int value)
+{
+    bool result = false;
+    for (int i = 0; i < length; ++i) {
+        if (set[i] == value) {
+            result = true;
+            break;
+        }
+    }
+    return result;
+}
+
+/**
+ * Check if the supplied array represents set,
+ *   i.e., if every value is unique
+ *
+ * @param set Integer array representing a set
+ * @param length Length of the provided array
+ *
+ * @return true when the provided `set` is an actual set;
+ *    false otherwise
+ */
+bool is_set(int set[], int length)
+{
+    bool result = true;
+    int intermediary[length];
+    for (int i = 0; i < length; ++i) {
+        intermediary[i] = 0;
+    }
+    bool hadZero = false;
+    for (int i = 0; i < length; ++i) {
+        if (set[i] == 0 && !hadZero) {
+            hadZero = true;
+        } else if (is_in_set(intermediary, length, set[i]) || (set[i] == 0 && hadZero)) {
+            result = false;
+            break;
+        } else {
+            intermediary[i] = set[i];
+        }
+    }
+    return result;
+}
+
+/**
+ * Check if the supplied array is a more effective representation of set,
+ *   i.e., every value is unique and the values are sorted
+ *
+ * @param set Integer array representing a set
+ * @param length Length of the provided array
+ *
+ * @return true when the provided set is sorted;
+ *    false otherwise
+ */
+bool is_sorted_set(int set[], int length)
+{
+    if (!is_set(set, length)) {
+        return false;
+    }
+    bool result = true;
+    for (int outer = 0; outer < length; ++outer) {
+        // check sort from lowest to higheest
+        for (int inner = outer; inner != 0; --inner) {
+            if (set[inner] > set[outer]) {
+                result = false;
+                break;
+            }
+        }
+
+        if (!result) {
+            break; // break if result is already false
+        }
+    }
+    return result;
+}
+
+/**
+ * Print an intersection of set1 and set2
+ *
+ * @param set1 First integer array representing a set
+ * @param set1_length Length of the first provided array
+ * @param set2 Second integer array representing a set
+ * @param set2_length Length of the second provided array
+ */
+void print_intersection(int set1[], int set2[], int set1_length, int set2_length)
+{
+    printf("{");
+    for (int i = 0; i < set1_length; ++i) {
+        if (is_in_set(set2, set2_length, set1[i])) {
+            printf("%d, ", set1[i]);
+        }
+    }
+    printf("}\n");
+}
+
+/**
+ * Print union of set1 and set2
+ *
+ * @param set1 First integer array representing a set
+ * @param set1_length Length of the first provided array
+ * @param set2 Second integer array representing a set
+ * @param set2_length Length of the second provided array
+ */
+void print_union(int set1[], int set2[], int set1_length, int set2_length)
+{
+    printf("{");
+    for (int i = 0; i < set1_length; ++i) {
+        printf("%d, ", set1[i]);
+    }
+    for (int i = 0; i < set2_length; ++i) {
+        if (!is_in_set(set1, set1_length, set2[i])) { // don't print duplicate values
+            printf("%d, ", set2[i]);
+        }
+    }
+    printf("}\n");
+}
+
+/**
+ * Print cartesian product of set1 and set2
+ *
+ * @param set1 First integer array representing a set
+ * @param set1_length Length of the first provided array
+ * @param set2 Second integer array representing a set
+ * @param set2_length Length of the second provided array
+ */
+void print_product(int set1[], int set2[], int set1_length, int set2_length)
+{
+    printf("{");
+    for (int i = 0; i < set1_length; ++i) {
+        for (int j = 0; j < set2_length; ++j) {
+            printf("(%d, %d), ", set1[i], set2[j]);
+        }
+    }
+    printf("}\n");
+}
+
+#ifndef TEST_BUILD
+
+#define SET_LENGTH 5
+
+int main()
+{
+    int set1[SET_LENGTH];
+    int set2[SET_LENGTH];
+
+    // Some example inputs (also try to switch set1 and set2!):
+    // int set1 = {5, 1, 7, 3, 8}
+    // int set2 = {4, 10, 6, 8, 5}
+    // ----
+    // int set1 = {1, 3, 5, 7, 8}
+    // int set2 = {4, 5, 6, 8, 10}
+    // ----
+    // int set1 = {1, 3, 4, 5, 9}
+    // int set2 = {2, 6, 7, 8, 10}
+
+    printf("Please specify a set (%d numbers): ", SET_LENGTH);
+    for (int i = 0; i < SET_LENGTH; i++) {
+        scanf("%d", &set1[i]);
+    }
+    // Only test that the array values are unique
+    if (!is_set(set1, SET_LENGTH)) {
+        printf("Error: the set contains duplicate values!\n");
+        return 1;
+    }
+    if (!is_sorted_set(set1, SET_LENGTH)) {
+        printf("Info: the set is not sorted!\n");
+    }
+
+    printf("Please specify a set (%d numbers): ", SET_LENGTH);
+    for (int i = 0; i < SET_LENGTH; i++) {
+        scanf("%d", &set2[i]);
+    }
+    // Only test that the array values are unique
+    if (!is_set(set2, SET_LENGTH)) {
+        printf("Error: the set contains duplicate values!\n");
+        return 1;
+    }
+    if (!is_sorted_set(set2, SET_LENGTH)) {
+        printf("Info: the set is not sorted!\n");
+    }
+
+    // Since the set do not have to be sorted, use inefficient versions
+    printf("Intersection: ");
+    print_intersection(set1, set2, SET_LENGTH, SET_LENGTH);
+    printf("Union:        ");
+    print_union(set1, set2, SET_LENGTH, SET_LENGTH);
+    printf("Product:      ");
+    print_product(set1, set2, SET_LENGTH, SET_LENGTH);
+    printf("\n");
+
+    return 0;
+}
+
+#endif