diff --git a/sk2/Makefile b/sk2/Makefile
new file mode 100644
index 0000000..1ea0871
--- /dev/null
+++ b/sk2/Makefile
@@ -0,0 +1,18 @@
+CC=gcc
+CFLAGS=-std=c11 -Wall -Wextra -O2
+LDFLAGS=-lm
+
+all: calc
+
+calc: main.o calculator.o
+	$(CC) $(CFLAGS) -o calc main.o calculator.o $(LDFLAGS)
+
+main.o: main.c calculator.h
+	$(CC) $(CFLAGS) -c main.c
+
+calculator.o: calculator.c calculator.h
+	$(CC) $(CFLAGS) -c calculator.c
+
+clean:
+	rm -f *.o calc
+
diff --git a/sk2/README.MD b/sk2/README.MD
new file mode 100644
index 0000000..d23eda7
--- /dev/null
+++ b/sk2/README.MD
@@ -0,0 +1,59 @@
+# Vedecká kalkulačka Matej Hajduk 
+
+## Zadanie
+Naprogramovať vedeckú kalkulačku, ktorá vyhodnocuje matematické výrazy v infixnej notácii.
+Kalkulačka musí podporovať:
+
+- načítanie a prácu s číslami s presnosťou min. 2 desatinné miesta
+- sčítanie, odčítanie, násobenie, delenie
+-zátvorky
+- funkcie: sinus, cosinus, odmocnina, druhá mocnina, logaritmus
+
+Príklad:
+- (2 + 3) * 2 -> 10
+- (10 * 2) + (6 / 2) -> 23
+
+
+## Stručný opis funkčnosti
+Program číta matematické výrazy zo štandardného vstupu (každý výraz na samostatnom riadku).
+Pre každý výraz vypočíta výsledok a vypíše ho na štandardný výstup.
+
+-pri chybe vypíše hlášku na stderr
+-podporuje aj zložitejšie výrazy so zátvorkami
+-podporuje aj unárne mínus (napr. -3*(2+1))
+
+## Stručný opis riešenia
+Riešenie je rozdelené na 3 časti:
+
+1. Tokenizácia
+   -rozdelenie vstupného reťazca na tokeny (čísla, operátory, funkcie, zátvorky)
+
+2. Prevod infix -> postfix
+   -použitý algoritmus Shunting-yard
+   -rieši priority operátorov a zátvorky
+
+3. Vyhodnotenie postfixu
+   -postfixový výraz sa vyhodnotí pomocou zásobníka (stack)
+   -pracuje sa s typom double
+
+## Podmienky za ktorých program funguje
+- výrazy musia byť syntakticky správne (napr. správne zátvorky)
+- podporované operátory: + - * / ^
+-podporované funkcie: sin(x), cos(x), sqrt(x), log(x), ln(x)
+- podporované konštanty: pi, e
+- sin a cos používajú radiány
+- log(x) je log10(x)
+- delenie nulou je ošetrené ako chyba
+-doménové chyby:
+  - sqrt(x) vyžaduje x >= 0
+  - log(x) a ln(x) vyžadujú x > 0
+
+## Použité zdroje
+-Matej Hajduk (implementácia)
+- ChatGPT (GPT-5.2), branch: sk2 (pomoc pri návrhu)
+- Shunting-yard algoritmus (infix -> postfix)
+-dokumentácia C:
+  - math.h (sin, cos, sqrt, log, log10, pow)
+  - strtod() (parsovanie čísiel)
+-geek4geeks
+
diff --git a/sk2/calculator.c b/sk2/calculator.c
new file mode 100644
index 0000000..330ff60
--- /dev/null
+++ b/sk2/calculator.c
@@ -0,0 +1,475 @@
+#include "calculator.h"
+#include <ctype.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* ---------------------------- */
+/* - globalna chyba             */
+/* ---------------------------- */
+static char g_err[128] = "OK";
+
+/* - helper: set error */
+static void set_err(const char *msg) {
+    strncpy(g_err, msg, sizeof(g_err)-1);
+}
+
+/* - vrat error text */
+const char *calc_error(void) {
+    return g_err;
+}
+
+/* ---------------------------- */
+/* - token typy                 */
+/* ---------------------------- */
+typedef enum {
+    T_NUM,      /* - cislo */
+    T_OP,       /* - operator */
+    T_FUNC,     /* - funkcia */
+    T_LP,       /* - ( */
+    T_RP        /* - ) */
+} TType;
+
+typedef struct {
+    TType type;
+    double num;      /* - hodnota */
+    char op;         /* - + - * / ^ ~ */
+    char func[8];    /* - sin cos sqrt log ln */
+} Token;
+
+/* ---------------------------- */
+/* - jednoduche pole tokenov    */
+/* ---------------------------- */
+typedef struct {
+    Token *a;
+    int n;
+    int cap;
+} TVec;
+
+/* - init */
+static void tvec_init(TVec *v) { v->a=NULL; v->n=0; v->cap=0; }
+
+/* - free */
+static void tvec_free(TVec *v) { free(v->a); tvec_init(v); }
+
+/* - push */
+static int tvec_push(TVec *v, Token t) {
+    if (v->n >= v->cap) {
+        int nc = v->cap ? v->cap*2 : 32;
+        Token *p = realloc(v->a, nc*sizeof(Token));
+        if (!p) return 0;
+        v->a = p;
+        v->cap = nc;
+    }
+    v->a[v->n++] = t;
+    return 1;
+}
+
+/* ---------------------------- */
+/* - priorita operatorov        */
+/* ---------------------------- */
+static int prec(char op) {
+    if (op=='~') return 4; /* - unarne minus */
+    if (op=='^') return 3; /* - mocnina */
+    if (op=='*' || op=='/') return 2; /* - nasob/del */
+    if (op=='+' || op=='-') return 1; /* - plus/minus */
+    return -1;
+}
+
+/* - prava asociativita */
+static int right_assoc(char op) {
+    return (op=='^' || op=='~'); /* - pow, unary */
+}
+
+/* ---------------------------- */
+/* - tokenize: string -> tokeny */
+/* ---------------------------- */
+static int tokenize(const char *s, TVec *out) {
+    /* - reset error */
+    set_err("OK");
+
+    tvec_init(out);
+
+    /* - prev token */
+    TType prev = T_OP; /* - na zaciatku */
+
+    while (*s) {
+        /* - skip spaces */
+        while (isspace((unsigned char)*s)) s++;
+
+        if (!*s) break;
+
+        /* ---------------------------- */
+        /* - cislo                      */
+        /* ---------------------------- */
+        if (isdigit((unsigned char)*s) || *s=='.') {
+            char *end = NULL;
+            double x = strtod(s, &end);
+            if (end==s) { set_err("Zle cislo"); return 0; }
+
+            Token t = {0};
+            t.type = T_NUM;
+            t.num = x;
+
+            if (!tvec_push(out, t)) { set_err("No memory"); return 0; }
+
+            s = end;
+            prev = T_NUM;
+            continue;
+        }
+
+        /* ---------------------------- */
+        /* - ident: funkcia/konstanta    */
+        /* ---------------------------- */
+        if (isalpha((unsigned char)*s)) {
+            char buf[16]={0};
+            int i=0;
+
+            while (isalpha((unsigned char)*s) && i<15) {
+                buf[i++] = (char)tolower((unsigned char)*s);
+                s++;
+            }
+            buf[i]=0;
+
+            /* - konstanta pi */
+            if (!strcmp(buf,"pi")) {
+                Token t={0};
+                t.type=T_NUM;
+                t.num=M_PI;
+                if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+                prev=T_NUM;
+                continue;
+            }
+
+            /* - konstanta e */
+            if (!strcmp(buf,"e")) {
+                Token t={0};
+                t.type=T_NUM;
+                t.num=M_E;
+                if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+                prev=T_NUM;
+                continue;
+            }
+
+            /* - funkcie */
+            if (!strcmp(buf,"sin") || !strcmp(buf,"cos") ||
+                !strcmp(buf,"sqrt") || !strcmp(buf,"log") ||
+                !strcmp(buf,"ln")) {
+
+                Token t={0};
+                t.type=T_FUNC;
+                strncpy(t.func, buf, sizeof(t.func)-1);
+
+                if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+                prev=T_FUNC;
+                continue;
+            }
+
+            set_err("Neznama funkcia");
+            return 0;
+        }
+
+        /* ---------------------------- */
+        /* - zatvorky                   */
+        /* ---------------------------- */
+        if (*s=='(') {
+            Token t={0};
+            t.type=T_LP;
+            if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+            s++;
+            prev=T_LP;
+            continue;
+        }
+
+        if (*s==')') {
+            Token t={0};
+            t.type=T_RP;
+            if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+            s++;
+            prev=T_RP;
+            continue;
+        }
+
+        /* ---------------------------- */
+        /* - operatory                  */
+        /* ---------------------------- */
+        if (strchr("+-*/^", *s)) {
+            char op = *s;
+
+            /* - unary minus */
+            if (op=='-' && !(prev==T_NUM || prev==T_RP)) {
+                op='~';
+            }
+
+            Token t={0};
+            t.type=T_OP;
+            t.op=op;
+
+            if (!tvec_push(out,t)) { set_err("No memory"); return 0; }
+
+            s++;
+            prev=T_OP;
+            continue;
+        }
+
+        set_err("Neplatny znak");
+        return 0;
+    }
+
+    if (out->n==0) { set_err("Prazdny vyraz"); return 0; }
+
+    return 1;
+}
+
+/* ---------------------------- */
+/* - infix -> postfix           */
+/* ---------------------------- */
+static int to_postfix(const TVec *in, TVec *out) {
+    tvec_init(out);
+
+    TVec st; /* - operator stack */
+    tvec_init(&st);
+
+    for (int i=0;i<in->n;i++) {
+        Token t = in->a[i];
+
+        /* - cislo -> output */
+        if (t.type==T_NUM) {
+            if (!tvec_push(out,t)) { set_err("No memory"); goto fail; }
+        }
+
+        /* - funkcia -> stack */
+        else if (t.type==T_FUNC) {
+            if (!tvec_push(&st,t)) { set_err("No memory"); goto fail; }
+        }
+
+        /* - operator */
+        else if (t.type==T_OP) {
+            while (st.n>0) {
+                Token top = st.a[st.n-1];
+
+                /* - funkcia ma prioritu */
+                if (top.type==T_FUNC) {
+                    if (!tvec_push(out,top)) { set_err("No memory"); goto fail; }
+                    st.n--;
+                    continue;
+                }
+
+                /* - operator priorita */
+                if (top.type==T_OP) {
+                    int p1 = prec(t.op);
+                    int p2 = prec(top.op);
+
+                    /* - pop pri vacsej priorite */
+                    if (p2>p1 || (p2==p1 && !right_assoc(t.op))) {
+                        if (!tvec_push(out,top)) { set_err("No memory"); goto fail; }
+                        st.n--;
+                        continue;
+                    }
+                }
+                break;
+            }
+            if (!tvec_push(&st,t)) { set_err("No memory"); goto fail; }
+        }
+
+        /* - ( -> stack */
+        else if (t.type==T_LP) {
+            if (!tvec_push(&st,t)) { set_err("No memory"); goto fail; }
+        }
+
+        /* - ) -> pop do ( */
+        else if (t.type==T_RP) {
+            int ok=0;
+
+            while (st.n>0) {
+                Token top = st.a[--st.n];
+
+                if (top.type==T_LP) { ok=1; break; }
+
+                if (!tvec_push(out,top)) { set_err("No memory"); goto fail; }
+            }
+
+            if (!ok) { set_err("Zle zatvorky"); goto fail; }
+
+            /* - po zatvorke funkcia */
+            if (st.n>0 && st.a[st.n-1].type==T_FUNC) {
+                Token f = st.a[--st.n];
+                if (!tvec_push(out,f)) { set_err("No memory"); goto fail; }
+            }
+        }
+    }
+
+    /* - pop zvysok */
+    while (st.n>0) {
+        Token top = st.a[--st.n];
+        if (top.type==T_LP) { set_err("Zle zatvorky"); goto fail; }
+        if (!tvec_push(out,top)) { set_err("No memory"); goto fail; }
+    }
+
+    tvec_free(&st);
+    return 1;
+
+fail:
+    tvec_free(&st);
+    tvec_free(out);
+    return 0;
+}
+
+/* ---------------------------- */
+/* - stack double               */
+/* ---------------------------- */
+typedef struct {
+    double *a;
+    int n;
+    int cap;
+} DStack;
+
+static void ds_init(DStack *s){ s->a=NULL; s->n=0; s->cap=0; }
+static void ds_free(DStack *s){ free(s->a); ds_init(s); }
+
+static int ds_push(DStack *s, double x){
+    if (s->n>=s->cap){
+        int nc=s->cap? s->cap*2:32;
+        double *p=realloc(s->a,nc*sizeof(double));
+        if(!p) return 0;
+        s->a=p; s->cap=nc;
+    }
+    s->a[s->n++]=x;
+    return 1;
+}
+
+static int ds_pop(DStack *s, double *x){
+    if(s->n==0) return 0;
+    *x=s->a[--s->n];
+    return 1;
+}
+
+/* ---------------------------- */
+/* - apply function             */
+/* ---------------------------- */
+static int apply_func(const char *f, double x, double *out){
+    if(!strcmp(f,"sin")) { *out=sin(x); return 1; }
+    if(!strcmp(f,"cos")) { *out=cos(x); return 1; }
+
+    if(!strcmp(f,"sqrt")){
+        if(x<0) { set_err("sqrt domena"); return 0; }
+        *out=sqrt(x);
+        return 1;
+    }
+
+    if(!strcmp(f,"log")){
+        if(x<=0) { set_err("log domena"); return 0; }
+        *out=log10(x);
+        return 1;
+    }
+
+    if(!strcmp(f,"ln")){
+        if(x<=0) { set_err("ln domena"); return 0; }
+        *out=log(x);
+        return 1;
+    }
+
+    set_err("Zla funkcia");
+    return 0;
+}
+
+/* ---------------------------- */
+/* - eval postfix               */
+/* ---------------------------- */
+static int eval_postfix(const TVec *post, double *out){
+    DStack st;
+    ds_init(&st);
+
+    for(int i=0;i<post->n;i++){
+        Token t=post->a[i];
+
+        /* - cislo -> push */
+        if(t.type==T_NUM){
+            if(!ds_push(&st,t.num)){ set_err("No memory"); goto fail; }
+        }
+
+        /* - funkcia */
+        else if(t.type==T_FUNC){
+            double a,r;
+            if(!ds_pop(&st,&a)){ set_err("Syntax"); goto fail; }
+            if(!apply_func(t.func,a,&r)) goto fail;
+            if(!ds_push(&st,r)){ set_err("No memory"); goto fail; }
+        }
+
+        /* - operator */
+        else if(t.type==T_OP){
+
+            /* - unary minus */
+            if(t.op=='~'){
+                double a;
+                if(!ds_pop(&st,&a)){ set_err("Syntax"); goto fail; }
+                if(!ds_push(&st,-a)){ set_err("No memory"); goto fail; }
+                continue;
+            }
+
+            /* - binarne */
+            double b,a,r;
+            if(!ds_pop(&st,&b) || !ds_pop(&st,&a)){ set_err("Syntax"); goto fail; }
+
+            if(t.op=='+') r=a+b;
+            else if(t.op=='-') r=a-b;
+            else if(t.op=='*') r=a*b;
+            else if(t.op=='/'){
+                if(b==0){ set_err("Delenie nulou"); goto fail; }
+                r=a/b;
+            }
+            else if(t.op=='^'){
+                r=pow(a,b);
+                if(isnan(r) || isinf(r)){ set_err("Pow domena"); goto fail; }
+            }
+            else { set_err("Zly operator"); goto fail; }
+
+            if(!ds_push(&st,r)){ set_err("No memory"); goto fail; }
+        }
+        else{
+            set_err("Syntax");
+            goto fail;
+        }
+    }
+
+    /* - musi ostat 1 */
+    if(st.n!=1){ set_err("Syntax"); goto fail; }
+
+    *out=st.a[0];
+    ds_free(&st);
+    return 1;
+
+fail:
+    ds_free(&st);
+    return 0;
+}
+
+/* ---------------------------- */
+/* - hlavna funkcia             */
+/* ---------------------------- */
+calc_status_t calc_evaluate(const char *expr, double *out){
+    if(!expr || !out){ set_err("NULL"); return CALC_ERR; }
+
+    TVec toks, post;
+    tvec_init(&toks);
+    tvec_init(&post);
+
+    /* - tokenize */
+    if(!tokenize(expr,&toks)){ tvec_free(&toks); return CALC_ERR; }
+
+    /* - postfix */
+    if(!to_postfix(&toks,&post)){ tvec_free(&toks); return CALC_ERR; }
+
+    /* - eval */
+    if(!eval_postfix(&post,out)){
+        tvec_free(&toks);
+        tvec_free(&post);
+        return CALC_ERR;
+    }
+
+    tvec_free(&toks);
+    tvec_free(&post);
+    return CALC_OK;
+}
+
diff --git a/sk2/calculator.h b/sk2/calculator.h
new file mode 100644
index 0000000..1dab3db
--- /dev/null
+++ b/sk2/calculator.h
@@ -0,0 +1,18 @@
+#ifndef CALCULATOR_H
+#define CALCULATOR_H
+
+typedef enum {
+    CALC_OK = 0,
+    CALC_ERR
+} calc_status_t;
+
+/* - vyhodnoti vyraz */
+/* - expr: vstup */
+/* - out: vysledok */
+calc_status_t calc_evaluate(const char *expr, double *out);
+
+/* - text chyby */
+const char *calc_error(void);
+
+#endif
+
diff --git a/sk2/main.c b/sk2/main.c
new file mode 100644
index 0000000..695e61a
--- /dev/null
+++ b/sk2/main.c
@@ -0,0 +1,35 @@
+#include "calculator.h"
+#include <math.h>
+#include <stdio.h>
+
+/* - pekny vypis */
+static void print_double(double x){
+    /* - cele cislo */
+    if (fabs(x - round(x)) < 1e-9) {
+        printf("%.0f\n", round(x));
+        return;
+    }
+    /* - min 2 des */
+    printf("%.2f\n", x);
+}
+
+int main(void){
+    char line[512];
+
+    /* - citaj riadky */
+    while (fgets(line,sizeof(line),stdin)){
+        double res;
+
+        /* - vypocitaj */
+        if (calc_evaluate(line,&res) != CALC_OK){
+            fprintf(stderr,"Chyba: %s\n", calc_error());
+            continue;
+        }
+
+        /* - vypis */
+        print_double(res);
+    }
+
+    return 0;
+}
+