diff --git a/semester1/pset13/2-1-malloc.c b/semester1/pset13/2-1-malloc.c
new file mode 100644
index 0000000..cf8f5c1
--- /dev/null
+++ b/semester1/pset13/2-1-malloc.c
@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void) {
+  int n;
+	scanf("%d", &n);
+	int *arr = malloc(n * sizeof(int));
+
+	for (int i = 0; i < n; i++) {
+		scanf("%d", &arr[i]);
+	}
+
+	for (int i = 0; i < n; i++) {
+		arr[i] = arr[i] * -10;
+	}
+
+	for (int i = 0; i < n - 1; i++) {
+		printf("%d ", arr[i]);
+	}
+	printf("%d\n", arr[n - 1]);
+
+	free(arr);
+  return 0;
+}
diff --git a/semester1/pset13/2-2-malloc2d.c b/semester1/pset13/2-2-malloc2d.c
new file mode 100644
index 0000000..67c4322
--- /dev/null
+++ b/semester1/pset13/2-2-malloc2d.c
@@ -0,0 +1,32 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void) {
+  int row, col;
+  scanf("%d%d", &row, &col);
+  // Initialize the 2d array
+  int **arr = malloc(sizeof(int *) * row);
+  for (int i = 0; i < row; i++) {
+    arr[i] = malloc(sizeof(int) * col);
+  }
+
+  for (int i = 0; i < row; i++) {
+    for (int j = 0; j < col; j++) {
+      scanf("%d", &arr[i][j]);
+    }
+  }
+
+  for (int i = 0; i < row; i++) {
+    for (int j = 0; j < col - 1; j++) {
+      printf("%d ", arr[i][j] * -10);
+    }
+    printf("%d\n", arr[i][col - 1] * -10);
+  }
+
+  // Free the 2d array
+  for (int i = 0; i < row; i++) {
+    free(arr[i]);
+  }
+  free(arr);
+  return 0;
+}
diff --git a/semester1/pset13/2-3-ArrayEX.c b/semester1/pset13/2-3-ArrayEX.c
new file mode 100644
index 0000000..58baa96
--- /dev/null
+++ b/semester1/pset13/2-3-ArrayEX.c
@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#define MAX 100001
+
+void sort(char **arr, int n);
+void swap(char **arr1, char **arr2);
+
+int main(void) {
+  int n;
+  scanf("%d", &n);
+  getchar();
+  // 2d array
+  char **str = malloc(sizeof(char *) * n);
+  // Buffer array
+  char *buffer = malloc(sizeof(char) * MAX);
+
+  for (int i = 0; i < n; i++) {
+    fgets(buffer, MAX, stdin);
+    str[i] = malloc(strlen(buffer) + 1);
+    strcpy(str[i], buffer);
+  }
+
+  sort(str, n);
+
+  for (int i = 0; i < n; i++) {
+    printf("%s", str[i]);
+  }
+
+  // Free up memory
+  free(buffer);
+  for (int i = 0; i < n; i++) {
+    free(str[i]);
+  }
+  free(str);
+  return 0;
+}
+
+void sort(char **arr, int n) {
+  for (int i = 0; i < n; i++) {
+    for (int j = 0; j < n - 1; j++) {
+      if (strcmp(arr[j], arr[j + 1]) > 0) {
+				// Why I can't use swap() here?
+        char *tmp = arr[j];
+        arr[j] = arr[j + 1];
+        arr[j + 1] = tmp;
+      }
+    }
+  }
+}
diff --git a/semester1/pset13/2-4-ArrayEX.c b/semester1/pset13/2-4-ArrayEX.c
new file mode 120000
index 0000000..6104f4b
--- /dev/null
+++ b/semester1/pset13/2-4-ArrayEX.c
@@ -0,0 +1 @@
+2-3-ArrayEX.c
\ No newline at end of file