C Strings

String Fundamentals

char str[10] = "Hello";

char str[] = {'H','i','\0'};

int len = strlen("Hello");

strcpy(dest, source);

🔹 String Declaration and Initialization

Strings in C are character arrays terminated with a null character '\0' that marks the string's end. Declare and initialize strings using char str[] = "Hello"; or char str[10] = "Hello"; to set fixed buffer sizes. The compiler automatically adds the null terminator. Understanding proper string declaration prevents buffer overflow vulnerabilities and ensures strings function correctly with standard library functions designed for null-terminated strings.

// Method 1: Character array with size
char str1[20] = "Hello";

// Method 2: Let compiler determine size
char str2[] = "World";

// Method 3: Character by character
char str3[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

// Method 4: Initialize empty string
char str4[50] = "";  // Empty string

// Method 5: String literal (read-only)
char *str5 = "Constant string";

🔹 String Input and Output

Reading and displaying strings uses functions like scanf(), gets(), fgets(), and printf(). Use scanf("%s", str) for simple input or fgets(str, size, stdin) for safer buffered input with size limits. Output strings using printf("%s", str) or puts(str). Proper input/output handling prevents security issues and enables interactive programs that communicate effectively with users.

#include <stdio.h>

int main() {
    char name[50];
    char message[100];
    
    // Output strings
    printf("Enter your name: ");
    
    // Input methods
    scanf("%s", name);          // Reads until space
    getchar();                  // Consume newline
    
    printf("Enter a message: ");
    fgets(message, 100, stdin); // Reads entire line
    
    // Output
    printf("Hello, %s!\n", name);
    printf("Your message: %s", message);
    
    return 0;
}

🔹 String Manipulation

Manipulating individual characters in strings involves accessing them by index and modifying their values. Use str[i] = character to change characters at specific positions, or iterate through the string using loops. Common manipulations include converting cases, replacing characters, or building new strings character-by-character. Understanding character-level manipulation enables creating utilities for text transformation and pattern processing in C.

#include <stdio.h>
#include <string.h>

int main() {
    char str[] = "Programming";
    
    // Access individual characters
    printf("First character: %c\n", str[0]);        // P
    printf("Last character: %c\n", str[10]);        // g
    
    // Modify characters
    str[0] = 'p';  // Change P to p
    printf("Modified string: %s\n", str);           // programming
    
    // String length
    printf("Length: %d\n", strlen(str));            // 11
    
    // Loop through characters
    printf("Characters: ");
    for(int i = 0; str[i] != '\0'; i++) {
        printf("%c ", str[i]);
    }
    printf("\n");
    
    return 0;
}

🔹 Basic String Operations

Essential string operations without library functions teach fundamental programming concepts through manual implementation. Manually counting string length, copying strings character-by-character, concatenating strings, and comparing strings develop deeper understanding of C's string handling. These operations involve iterating through arrays with loops and null-terminator awareness. Learning basic operations strengthens your programming skills and clarifies how standard library functions work internally.

int stringLength(char str[]) {
    int length = 0;
    while(str[length] != '\0') {
        length++;
    }
    return length;
}

void copyString(char dest[], char source[]) {
    int i = 0;
    while(source[i] != '\0') {
        dest[i] = source[i];
        i++;
    }
    dest[i] = '\0';  // Add null terminator
}

int compareStrings(char str1[], char str2[]) {
    int i = 0;
    while(str1[i] != '\0' && str2[i] != '\0') {
        if(str1[i] != str2[i]) {
            return 0;  // Not equal
        }
        i++;
    }
    return (str1[i] == '\0' && str2[i] == '\0');
}

🔹 Common String Problems

Practice solving common string challenges like counting vowels, reversing strings, checking palindromes, and removing spaces. These exercises reinforce understanding of loops, conditional statements, and character manipulation. For example, reversing a string involves reading from end to beginning, counting vowels requires checking each character against a vowel set, and removing characters involves selectively copying characters. Solving these problems builds practical skills applicable to real-world text processing applications.

#include <stdio.h>

// Count vowels in a string
int countVowels(char str[]) {
    int count = 0;
    for(int i = 0; str[i] != '\0'; i++) {
        char c = str[i];
        if(c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u' ||
           c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U') {
            count++;
        }
    }
    return count;
}

// Reverse a string
void reverseString(char str[]) {
    int length = 0;
    while(str[length] != '\0') length++;  // Find length
    
    for(int i = 0; i < length/2; i++) {
        char temp = str[i];
        str[i] = str[length-1-i];
        str[length-1-i] = temp;
    }
}

int main() {
    char text[] = "Hello World";
    
    printf("Original: %s\n", text);
    printf("Vowels: %d\n", countVowels(text));
    
    reverseString(text);
    printf("Reversed: %s\n", text);
    
    return 0;
}