8. Strings

Working with null-terminated character arrays, string I/O, and common string functions in C.

Strings are arrays of char terminated by \0.

• Input/output with printf, scanf, fgets, puts
• Functions: strlen, strcpy, strcat, strcmp
• Examples: palindrome and word count

Examples

String Length (string_length.c)

Manually counts characters until \0, illustrating how C strings work internally:

#include <stdio.h>

int my_strlen(const char *s) {
    int c = 0;
    while (s[c] != '\0') c++;
    return c;
}

int main(void) {
    char text[100];
    printf("Enter text: ");
    if (fgets(text, sizeof text, stdin)) {
        int len = my_strlen(text);
        if (len > 0 && text[len-1] == '\n') text[len-1] = '\0';
        printf("Length = %d\n", my_strlen(text));
    }
    return 0;
}

Palindrome Check (palindrome_string.c)

Checks whether a word reads the same forward and backward:

#include <stdio.h>

int is_palindrome(const char *s) {
    int i = 0, j = 0;
    while (s[j] != '\0') j++;
    if (j > 0 && s[j-1] == '\n') j--;
    j--;
    while (i < j) {
        if (s[i] != s[j]) return 0;
        i++; j--;
    }
    return 1;
}

int main(void) {
    char text[100];
    printf("Enter a word: ");
    if (fgets(text, sizeof text, stdin)) {
        if (is_palindrome(text)) printf("Palindrome\n");
        else printf("Not a palindrome\n");
    }
    return 0;
}