diff --git a/DeitelC/Chapter4/NaturalNumberArithmetic.c b/DeitelC/Chapter4/NaturalNumberArithmetic.c
new file mode 100644
index 0000000..68a9426
--- /dev/null
+++ b/DeitelC/Chapter4/NaturalNumberArithmetic.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+int main(void) {
+    int i = 0, total = 0;
+    puts("Enter an integer!");
+    if(scanf("%d", &i)) {
+        for(int sum = 0; sum <= i; sum++) {
+            total += sum;
+        }
+        printf("Total sum: %d\n", total);
+        total = 0;
+        for(int sum = 0; sum * sum <= i * i; sum++) {
+            int pow = sum * sum;
+            total += pow;
+        }
+        printf("Sum of squares: %d\n", total);
+        total = 0;
+        for(int sum = 0; sum * sum * sum <= i * i * i; sum++) {
+            int pow = sum * sum * sum;
+            total += pow;
+        }
+        printf("Sum of cubes: %d\n", total);
+        } else {
+            puts("Enter valid integer!");
+        }
+}
diff --git a/DeitelC/Chapter4/a.exe b/DeitelC/Chapter4/a.exe
deleted file mode 100644
index 8c66b27..0000000
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diff --git a/DeitelC/Chapter4/a.out b/DeitelC/Chapter4/a.out
index d707f01..ee38609 100644
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diff --git a/DeitelC/Chapter4/factorial1to5.c b/DeitelC/Chapter4/factorial1to5.c
new file mode 100644
index 0000000..2859491
--- /dev/null
+++ b/DeitelC/Chapter4/factorial1to5.c
@@ -0,0 +1,11 @@
+#include <stdio.h>
+
+int main(void) {
+    puts("Factorial 1 to 5: ");
+    double sum = 1;
+    for(double i = 1; i <= 20; i++) {
+        sum *= i;
+        printf("The %0.lf! are: %0.lf\n", i, sum);
+    }
+    return 0;
+}
diff --git a/DeitelC/Chapter4/trianglePrinting.c b/DeitelC/Chapter4/trianglePrinting.c
new file mode 100644
index 0000000..d9a5339
--- /dev/null
+++ b/DeitelC/Chapter4/trianglePrinting.c
@@ -0,0 +1,11 @@
+#include <stdio.h>
+
+int main(void) {
+    int start = 10;
+    for(int i = 1; i <= start; i++) {
+        for(int j = 0; j <= i; j++){
+            printf("%s", "*");
+        }
+    }
+    printf("\n");
+}
diff --git a/a.out b/a.out
new file mode 100644
index 0000000..b86930d
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diff --git a/montyHall.c b/montyHall.c
new file mode 100644
index 0000000..972097a
--- /dev/null
+++ b/montyHall.c
@@ -0,0 +1,49 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+int main(void) {
+    srand(time(NULL));  // Seed random number generator
+    int r, s, openD;
+    int counter = 0, win = 0;
+
+    while (1) {
+        r = rand() % 3; // Winning door (0, 1, or 2)
+        s = -1;
+
+        puts("Select one of the 3 doors (0, 1, 2). Enter -1 to quit:");
+        scanf("%d", &s);
+        if (s == -1) break;
+
+        // Open a door with a goat (not the winning door or the selected door)
+        openD = rand() % 3;
+        while (openD == r || openD == s) {
+            openD = rand() % 3;
+        }
+
+        printf("You chose: %d, a goat is behind door: %d\n", s, openD);
+        puts("Do you want to choose another door? (Enter new door number):");
+        scanf("%d", &s);
+
+        while (s == openD) {
+            puts("This door is already opened! Select another door:");
+            scanf("%d", &s);
+        }
+
+        if (s == r) {
+            puts("YOU WON!");
+            win++;
+        } else {
+            puts("YOU LOSE!");
+        }
+        counter++;
+    }
+
+    if (counter > 0) {
+        printf("Win percentage: %d%%\n", (win * 100) / counter);
+    } else {
+        puts("No games played.");
+    }
+
+    return 0;
+}