8-dars: String — chuqur o'rganish

Dars haqida

Davomiyligi: 90 daqiqa Maqsad: Talaba string.h funksiyalarini chuqur o'rganishi, o'z string funksiyalarini yozishi va string algoritmlari bilan ishlay olishi kerak.

1. String — quick reminder

String = char massivi + \0.

char s[] = "Hello";  // {'H','e','l','l','o','\0'}

\0 — null terminator, string oxirini bildiradi.

2. string.h — barcha funksiyalar

#include <string.h>

Funksiya	Vazifa
strlen(s)	Uzunlik
strcpy(dst, src)	Nusxa olish
strncpy(dst, src, n)	n belgi
strcat(dst, src)	Qo'shish
strncat(dst, src, n)	n belgi qo'shish
strcmp(s1, s2)	Taqqoslash
strncmp(s1, s2, n)	n belgi taqqoslash
strchr(s, c)	Belgini topish
strrchr(s, c)	Oxirgi belgini topish
strstr(s, sub)	Substring topish
strtok(s, delim)	Bo'lish
memset(s, c, n)	n belgini c bilan to'ldirish
memcpy(dst, src, n)	n byte nusxa olish

3. strlen — chuqur

size_t strlen(const char *s) {
    size_t len = 0;
    while (s[len] != '\0') len++;
    return len;
}

size_t — unsigned int (manfiy emas).

Tezligi: O(n) — har safar oxirigacha o'tadi.

for (int i = 0; i < strlen(str); i++) {  // SEKIN!
    // strlen har iteration'da hisoblanadi
}

int len = strlen(str);
for (int i = 0; i < len; i++) {  // TEZ
    // bir marta hisoblandi
}

4. strcpy va strncpy

char dst[10];
strcpy(dst, "Hello");        // OK
strcpy(dst, "Hello World");  // BUFFER OVERFLOW

strncpy(dst, "Hello World", 9);
dst[9] = '\0';  // strncpy \0 qo'shmaydi

strcpy xavfli

Doim strncpy yoki snprintf ishlating.

5. strcat

char str[100] = "Hello ";
strcat(str, "World");
// str = "Hello World"

Hajmga e'tibor: dst yetarli bo'lsin.

char str[5] = "Hi ";
strcat(str, "World");  // BUFFER OVERFLOW!

6. strcmp natijasi

int n = strcmp("abc", "abd");
// n < 0 (c < d, alifboda)

int n = strcmp("abc", "abc");
// n == 0

int n = strcmp("abd", "abc");
// n > 0

Aniq qiymat — implementatsiyaga bog'liq. Faqat belgi muhim.

if (strcmp(a, b) == 0) {
    // teng
}

7. strchr va strstr

char str[] = "Hello World";

char *p = strchr(str, 'W');
// p ko'rsatadi 'W' ga
// p == str + 6
printf("%s\n", p);  // "World"

char *p2 = strstr(str, "World");
// p2 == str + 6

char *p3 = strstr(str, "xyz");
// p3 == NULL (topilmadi)

8. strtok — bo'lish

char str[] = "apple,banana,orange";
char *token = strtok(str, ",");

while (token != NULL) {
    printf("%s\n", token);
    token = strtok(NULL, ",");  // ikkinchidan boshlab — NULL
}

Natija:

apple
banana
orange

strtok original'ni o'zgartiradi

strtok — , o'rniga \0 qo'yadi. Original string buziladi.

Kerakli bo'lsa — nusxa oling.

9. O'zingizning string funksiyalaringiz

my_strlen

size_t my_strlen(const char *s) {
    size_t len = 0;
    while (*s != '\0') {
        len++;
        s++;
    }
    return len;
}

my_strcpy

char *my_strcpy(char *dst, const char *src) {
    char *start = dst;
    while ((*dst++ = *src++) != '\0');
    return start;
}

my_strcat

char *my_strcat(char *dst, const char *src) {
    char *start = dst;
    while (*dst != '\0') dst++;
    while ((*dst++ = *src++) != '\0');
    return start;
}

my_strcmp

int my_strcmp(const char *s1, const char *s2) {
    while (*s1 && (*s1 == *s2)) {
        s1++;
        s2++;
    }
    return *(unsigned char*)s1 - *(unsigned char*)s2;
}

10. String reverse

void reverse(char *s) {
    int len = strlen(s);
    for (int i = 0; i < len / 2; i++) {
        char temp = s[i];
        s[i] = s[len - 1 - i];
        s[len - 1 - i] = temp;
    }
}

// Yoki pointer bilan:
void reverse(char *s) {
    char *end = s;
    while (*end) end++;
    end--;
    
    while (s < end) {
        char t = *s;
        *s = *end;
        *end = t;
        s++;
        end--;
    }
}

11. So'z sanash

int count_words(const char *s) {
    int count = 0;
    int in_word = 0;
    
    while (*s) {
        if (*s == ' ' || *s == '\t' || *s == '\n') {
            in_word = 0;
        } else if (!in_word) {
            in_word = 1;
            count++;
        }
        s++;
    }
    return count;
}

12. Substring topish (manual)

char *my_strstr(const char *haystack, const char *needle) {
    if (*needle == '\0') return (char*)haystack;
    
    while (*haystack) {
        const char *h = haystack;
        const char *n = needle;
        
        while (*h && *n && *h == *n) {
            h++;
            n++;
        }
        
        if (*n == '\0') return (char*)haystack;
        haystack++;
    }
    return NULL;
}

13. Palindrome (string)

int is_palindrome(const char *s) {
    int len = strlen(s);
    for (int i = 0; i < len / 2; i++) {
        if (tolower(s[i]) != tolower(s[len - 1 - i])) {
            return 0;
        }
    }
    return 1;
}

14. Anagram tekshirish

Anagram — bir xil harflar bilan tuzilgan ikki so'z (listen va silent).

int is_anagram(const char *s1, const char *s2) {
    if (strlen(s1) != strlen(s2)) return 0;
    
    int count[256] = {0};
    
    while (*s1) {
        count[(unsigned char)*s1]++;
        s1++;
    }
    
    while (*s2) {
        count[(unsigned char)*s2]--;
        if (count[(unsigned char)*s2] < 0) return 0;
        s2++;
    }
    
    return 1;
}

15. String massivi sort

#include <string.h>

void sort_strings(char arr[][50], int n) {
    char temp[50];
    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - 1 - i; j++) {
            if (strcmp(arr[j], arr[j+1]) > 0) {
                strcpy(temp, arr[j]);
                strcpy(arr[j], arr[j+1]);
                strcpy(arr[j+1], temp);
            }
        }
    }
}

int main(void) {
    char names[][50] = {"Botir", "Akmal", "Dilshod", "Aziza"};
    sort_strings(names, 4);
    for (int i = 0; i < 4; i++) {
        printf("%s\n", names[i]);
    }
    return 0;
}

16. fgets va sscanf

scanf("%s", ...) — bo'shliqgacha o'qiydi.

To'liq qator uchun — fgets:

char buffer[100];
fgets(buffer, sizeof(buffer), stdin);
// buffer'da \n bor!

// \n ni olib tashlash
buffer[strcspn(buffer, "\n")] = '\0';

Keyin sscanf bilan tahlil:

char input[] = "Akmal 22 Toshkent";
char name[50], city[50];
int age;
sscanf(input, "%s %d %s", name, &age, city);

17. snprintf — xavfsiz print

char buffer[100];
snprintf(buffer, sizeof(buffer), "Yosh: %d, Ism: %s", 22, "Akmal");

Buffer'ga xavfsiz yozadi (overflow yo'q).

18. Edit distance — kirish

Edit distance (Levenshtein) — bir so'zni boshqasiga aylantirish uchun nechta o'zgartirish kerak.

"kitten" → "sitting"
1. kitten → sitten (k → s)
2. sitten → sittin (e → i)
3. sittin → sitting (qo'shish)

Edit distance = 3

Algoritm — keyingi darslarda.

Darsdagi topshiriqlar

1 — String funksiyalar

string-fn.c — Dars matnidagi barcha my_* funksiyalarini yozing va sinab ko'ring.

2 — Reverse

reverse.c — 2 ta versiya: index bilan va pointer bilan.

3 — Word counter

word-count.c:

char text[] = "Bu matn 5 ta so'z";
int n = count_words(text);  // 5

4 — Palindrome

palindrome.c — string uchun (bo'shliq va katta-kichik harflarni e'tiborsiz).

5 — Anagram

anagram.c — 2 ta so'z anagramami?

Sinab ko'ring:

• listen, silent → Ha
• hello, world → Yo'q
• evil, vile → Ha

6 — Substring count

count-substr.c:

int count_substring(const char *s, const char *sub);

Misol: "abababab" da "ab" — 4 marta.

7 — Tokenize

tokenize.c — strtok bilan:

char data[] = "Akmal,22,Toshkent,Talaba";
// 4 ta token: Akmal, 22, Toshkent, Talaba

8 — String sort

string-sort.c — ismlar massivini alfabit bo'yicha.

9 — Caesar cipher (yana)

4-oydagi Caesar'ni yaxshilang:

• Decryption funksiyasi
• Brute force (har shift sinab)
• Case sensitive

void caesar_encrypt(char *s, int shift);
void caesar_decrypt(char *s, int shift);
void caesar_bruteforce(const char *s);

10 — GitHub

$ mkdir 5-oy-dars-8
$ git add . && git commit -m "feat: dars 8 - strings deep" && git push

Lug'at

Termin	Izoh
string.h	String funksiyalari header
strlen	Uzunlik
strcpy / strncpy	Nusxalash
strcat / strncat	Qo'shish
strcmp / strncmp	Taqqoslash
strchr / strstr	Topish
strtok	Bo'lish
memset / memcpy	Memory functions
snprintf	Xavfsiz print
fgets	Qator olish
Anagram	Bir xil harflar bilan
Edit distance	Levenshtein masofa

Keyingi dars

9-dars: Struct asoslari →