diff --git a/du1/program.c b/du1/program.c
index f3d90e1..f422624 100644
--- a/du1/program.c
+++ b/du1/program.c
@@ -10,6 +10,9 @@ struct pizza{
 	float prize;
 	char name[LINE_SIZE];
 };
+/* structura jednej polozky*/
+
+
 
 char hacker_script(char c){
 	c = tolower((unsigned char)c);
@@ -26,15 +29,17 @@ char hacker_script(char c){
         case '9': return 'q';
         default: return c;}
 }
+/*hacker script nam bude vymenovat cisla na bukvy*/
+
 
 
 void normalize(const char *source, char *dest){
 	int i =0;
-	while(source[i]!='\0'){
-		dest[i]= hacker_script(source[i]);
+	while(source[i]!='\0'){				/* tu je cyklus ktory precahdza slovom a normalizuje ho*/
+		dest[i]= hacker_script(source[i]); 
 		i++;
 	}
-	dest[i]='\0';
+	dest[i]='\0'; ///ked slovo konci, cyklus tiez skonci a na konci bude terminator
 }
 
 
@@ -42,21 +47,22 @@ void normalize(const char *source, char *dest){
 
 
 
-int read_pizza(struct pizza *item){
-	char line_1[LINE_SIZE];
-	char line_2[LINE_SIZE];
 
-	if (fgets(line_1,LINE_SIZE,stdin)==NULL) return 0;
+int read_pizza(struct pizza *item){
+	char line_1[LINE_SIZE]; /// pre name
+	char line_2[LINE_SIZE]; /// pre price
+
+	if (fgets(line_1,LINE_SIZE,stdin)==NULL) return 0; /// nacitava name, ak line_1 bude null tak nastala chyba
 	if (fgets(line_2,LINE_SIZE,stdin)==NULL) return 0;
 	
-	line_1[strcspn(line_1,"\n")] = '\0';
+	line_1[strcspn(line_1,"\n")] = '\0'; /// ukoncuje terminatorom
 	line_2[strcspn(line_2,"\n")] = '\0';
 	
 	float price = 0.0;
-	if (sscanf(line_2, "%f", &price)!=1) return 0;
+	if (sscanf(line_2, "%f", &price)!=1) return 0;// nacitava len float number
 
 	strcpy(item->name, line_1);
-	item->prize = price;
+	item->prize = price; // uklada name a price do itemu
 
 	return 1;
 }
@@ -66,29 +72,31 @@ int main(){
 	char search[LINE_SIZE];
 	char normal_search[LINE_SIZE];
 
-	struct pizza list[MAXIT];
-	int cnt = 0;
+	struct pizza list[MAXIT]; 
+	int cnt = 0; 
 	
 	printf("Zadaj hladanu surovinu:\n");
 	if (fgets(search, LINE_SIZE, stdin)==NULL) return 0;
 	search[strcspn(search,"\n")] = '\0';
 
-	normalize(search, normal_search);
+	normalize(search, normal_search); // normalizujeme nas hladany prvok
 	
 	printf("Zadaj jedalny listok:\n");
 
 
-	while(cnt<MAXIT&&read_pizza(&list[cnt])){ cnt++;}
+	while(cnt<MAXIT&&read_pizza(&list[cnt])){ cnt++;} // ak cnt menej ako MAXIT aj je nacitana jedna polozka
+	
 	for (int i =0;i<cnt; i++){
 		char normal_name[LINE_SIZE];
-		normalize(list[i].name, normal_name);
+		normalize(list[i].name, normal_name); // normalizujeme meno 
 		
-		if (strstr(normal_name, normal_search) != NULL) {
+		if (strstr(normal_name, normal_search) != NULL) { // ak mame to co hladame
             	printf("%s\n", list[i].name);
-            	printf("%.2f\n", list[i].prize);
+            	printf("%.2f\n", list[i].prize); // vyprintujeme
         	}
 
-	}
-	printf("Nacitanych %d poloziek.\n", cnt);
+	} // ak ne bude nic podobne, cyklus po nacitavani vsetkych poloziek ukonci
+
+	printf("Nacitanych %d poloziek.\n", cnt); // vypise cislo poloziek
 	return 0;
 }
diff --git a/du2/program.c b/du2/program.c
index 6340a43..e6a864b 100644
--- a/du2/program.c
+++ b/du2/program.c
@@ -13,19 +13,19 @@ struct pizza{
 
 
 int read_pizza(struct pizza *item){
-        char line_1[LINE_SIZE];
-        char line_2[LINE_SIZE];
+        char line_1[LINE_SIZE]; //nazov
+        char line_2[LINE_SIZE];//cena
 
-        if (fgets(line_1,LINE_SIZE,stdin)==NULL) return 0;
+        if (fgets(line_1,LINE_SIZE,stdin)==NULL) return 0;//ak nie je vstup return o
         if (fgets(line_2,LINE_SIZE,stdin)==NULL) return 0;
 
-        line_1[strcspn(line_1,"\n")] = '\0';
+        line_1[strcspn(line_1,"\n")] = '\0';//odstrani znak rovnakeho riadku
         line_2[strcspn(line_2,"\n")] = '\0';
 
         float price = 0.0;
-        if (sscanf(line_2, "%f", &price)!=1||price<=0) return 0;
+        if (sscanf(line_2, "%f", &price)!=1||price<=0) return 0;//kontrola vystupy
 
-        strcpy(item->name, line_1);
+        strcpy(item->name, line_1);// skopiruje nazov do struktury
         item->prize = price;
 
         return 1;
@@ -34,14 +34,14 @@ int read_pizza(struct pizza *item){
 
 int read_pizza_list(struct pizza* list){
 	int counter = 0;
-	for(int i = 0; i<MAXIT;i++){
-		struct pizza item;
-		memset(&item,0,sizeof(struct pizza));
-		int r = read_pizza(&item);
-		if (r){
-	    		memcpy(&list[counter], &item, sizeof(struct pizza));
-            		counter++;
-        	} else {
+	for(int i = 0; i<MAXIT;i++){ // cyklus nacitava vsetky pizzy 
+		struct pizza item; //pomocna premenna
+		memset(&item,0,sizeof(struct pizza)); // vydelime pamat
+		int r = read_pizza(&item); //nacitajme jednu pizzu
+		if (r){ // ak nacitana
+	    		memcpy(&list[counter], &item, sizeof(struct pizza)); // kopirujeme z itemu do naseho menu
+            		counter++; // cnt+1
+        	} else { // ak nie
             		break;
         	}
     	}
@@ -50,24 +50,24 @@ int read_pizza_list(struct pizza* list){
 
 
 int compare_pizza (const void * a, const void * b){
-	const struct pizza *p1 = (const struct pizza *)a;
-	const struct pizza *p2 = (const struct pizza *)b;
+	const struct pizza *p1 = (const struct pizza *)a; // pointer na prvu pizzu
+	const struct pizza *p2 = (const struct pizza *)b; // pointer na druhu 
 	
-	if(p1->prize<p2->prize) return -1;
+	if(p1->prize<p2->prize) return -1; 
 	if(p1->prize>p2->prize) return 1;
 
-	return strcmp(p1->name,p2->name);
+	return strcmp(p1->name,p2->name); // ak cena bude ta ista, porovname mena
 
 }
 
 
 int main(){
 	struct pizza list[MAXIT];
-	memset(list,0,sizeof(list));
+	memset(list,0,sizeof(list)); // vydelime pamat pre menu
 
 	int count = read_pizza_list(list);
 	
-	qsort(list,count,sizeof(struct pizza), compare_pizza);
+	qsort(list,count,sizeof(struct pizza), compare_pizza); //triedenie menu
 	for (int i = 0;i<count;i++){
 		printf("%s\n%.6f\n",list[i].name,list[i].prize);
 	}
diff --git a/du3/program.c b/du3/program.c
index 44c1d2d..acaf995 100644
--- a/du3/program.c
+++ b/du3/program.c
@@ -13,10 +13,10 @@ struct stack {
 
 
 void init(struct stack *s){
-    s->size=0;
+    s->size=0; //inicializacia stacku
 }
 
-int is_empty(struct stack *s){return s->size==0;}
+int is_empty(struct stack *s){return s->size==0;} // check if stack is empty
 int is_full(struct stack *s){return s->size==STACK_SIZE;}
 
 
@@ -25,7 +25,7 @@ void push(struct stack *s, float value){
         printf("full stack\n");
         exit(0);
     }
-    s->values[s->size++]=value;
+    s->values[s->size++]=value; // pridava cislo do stacku a size +=1
 }
 
 float pop (struct stack *s){
@@ -33,7 +33,7 @@ float pop (struct stack *s){
         printf("Stack is empty");
         return 1;
     }
-    return s->values[--(s->size)];
+    return s->values[--(s->size)]; // najprv - size, potom vybera jednu polozku
 }
 
 
@@ -55,13 +55,13 @@ int main(){
         input[strcspn(input,"\n")]='\0';
 
         char *endpt;
-        float num = strtod(input,&endpt);
+        float num = strtod(input,&endpt); // oddeli vsetky cisla (medzerami) a posledne zapise do endpt
 
-        if(endpt!=input&&*endpt=='\0'){
+        if(endpt!=input&&*endpt=='\0'){ // ked endpt!= plnomu inputu a nie je koncom inputu
             push(&mystack,num);
         }
-        else if (strlen(input)==1&&strchr("+-*/",input[0])){
-            if (mystack.size<2){
+        else if (strlen(input)==1&&strchr("+-*/",input[0])){ // ak dlzka inputu po upravach 1 a to nojeaky operator  
+            if (mystack.size<2){ // previerka na to ci mame cisla pre operacie
                 printf("not enough operands\n");
                 return 0;}
             float b=pop(&mystack);
diff --git a/du4/Makefile b/du4/Makefile
new file mode 100644
index 0000000..3c2c463
--- /dev/null
+++ b/du4/Makefile
@@ -0,0 +1,13 @@
+CFLAGS= -std=c99 -g -Wall
+
+all: train
+
+%.o: %.c
+	gcc -c -o $@ $< $(CFLAGS)
+
+train: main.o a_train.o
+	gcc main.o a_train.o -o train 
+
+clean:
+	rm *.o train
+
diff --git a/du4/a_train.c b/du4/a_train.c
new file mode 100644
index 0000000..004d27e
--- /dev/null
+++ b/du4/a_train.c
@@ -0,0 +1,58 @@
+#include "a_train.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct car* add_car(struct car* first,const char* target) {
+    	struct car* new = calloc(1, sizeof(struct car));
+	if(!new) return first;
+	strcpy(new->value,target);
+	if (first==NULL){
+		return new;
+	}
+	
+	struct car* sm = first;
+	while(sm->next!=NULL){
+		sm = sm->next;
+	}
+	sm->next = new;
+	return first;
+	
+}
+
+void print_train(struct car* first) {
+	struct car* hlp = first;
+	while(hlp!=NULL){
+		printf("Cielova stanica je %s\n",hlp->value);
+		hlp = hlp->next;
+	
+	}
+}
+
+
+void cancel_train(struct car* first) {
+	if(!first) return;
+	cancel_train(first->next);
+	free(first);
+}
+
+
+struct car* clear_train(struct car* first, const char* target) {
+	if(!first) return NULL;
+	if (strcmp(first->value, target)==0){
+		struct car* tmp = first->next;
+		free(first);
+		return tmp;
+	}
+	struct car* hlp = first;
+	while (hlp->next!=NULL&&strcmp(hlp->next->value,target)!=0){
+		hlp = hlp->next;
+	}
+	if (hlp->next!=NULL&&strcmp(hlp->next->value,target)==0){
+		struct car* del = hlp->next;
+		hlp->next=hlp->next->next;
+		free(del);
+	}
+	return first;
+}
+
diff --git a/du4/a_train.h b/du4/a_train.h
new file mode 100644
index 0000000..5982bfe
--- /dev/null
+++ b/du4/a_train.h
@@ -0,0 +1,51 @@
+#ifndef TRAIN_H
+#define TRAIN_H
+#define SIZE 100
+
+/**
+ * Jeden vozen vlaku
+ */
+struct car {
+    /**
+     * Nazov cielovej  stanice
+     */
+    char value[SIZE];
+    /**
+     * Smenik na dalsi vozen
+     */
+    struct car* next;
+};
+
+/**
+ * Prida vozen na koniec vlaku.
+ *
+ * @arg nazov cielovej stanice, ktory sa ma priradit novemu voznu.
+ * @return smernik na zaciatok vlaku.
+ */
+struct car* add_car(struct car* first,const char* target);
+
+
+/**
+ * Vypise vsetky vozne vo vlaku
+ *
+ * @arg smernik na prvy vozen
+ */
+void print_train(struct car* first);
+
+/**
+ * Zrusenie vsetkych voznov vo vlaku.
+ * @arg smernik na prvy vozen
+ */
+void cancel_train(struct car* first);
+
+/**
+ * Vyradenie vsetkych voznov, ktorych cielova stanica je target
+ *
+ * @arg smernik na prvy vozen
+ * @arg cielova stanica, ktora sa ma vyradit z vlaku.
+ * @return smernik na novy prvy vozen
+ *
+ */
+struct car* clear_train(struct car* first,const char* target);
+
+#endif // TRAIN_H
diff --git a/du4/a_train.o b/du4/a_train.o
new file mode 100644
index 0000000..07526f7
Binary files /dev/null and b/du4/a_train.o differ
diff --git a/du4/main.c b/du4/main.c
new file mode 100644
index 0000000..d64f05a
--- /dev/null
+++ b/du4/main.c
@@ -0,0 +1,17 @@
+#include "a_train.h"
+#include <stdio.h>
+
+// Testovaci subor pre vlak
+int main(){
+    struct car* train = NULL;
+    train = add_car(train,"Presov");
+    train = add_car(train,"Bratislava");
+    train = add_car(train,"Levoca");
+    train = add_car(train,"Spiska Nova Ves");
+    print_train(train);
+    clear_train(train,"Levoca");
+    print_train(train);
+    cancel_train(train);
+
+    return 0;
+}
diff --git a/du4/main.o b/du4/main.o
new file mode 100644
index 0000000..fbdc134
Binary files /dev/null and b/du4/main.o differ
diff --git a/du4/train b/du4/train
new file mode 100755
index 0000000..4a5e19d
Binary files /dev/null and b/du4/train differ