Data Structures and Algorithms in C (DSA)

📘 Strings – Manipulation & Inbuilt Functions

A string in C is a sequence of characters stored in an array of type char, and it is terminated by a special character '\0' (null character). Unlike other languages, strings in C are not a built-in data type — they are handled as arrays.

🔤 Declaring and Initializing Strings

char name[10];                   // Declaration
char greet[6] = {'H','e','l','l','o','\0'};  // Manual initialization
char str[] = "Hello";            // Automatic null-termination
  

📥 Input and Output for Strings

// Using scanf and gets
char name[50];
scanf("%s", name);       // Stops at space
// gets(name);           // (Unsafe: use fgets instead)

// Using fgets
fgets(name, sizeof(name), stdin); // Safe input
  

📌 Common String Functions (string.h)

• strlen(str) – Returns the length of the string
• strcpy(dest, src) – Copies one string into another
• strcat(dest, src) – Concatenates two strings
• strcmp(str1, str2) – Compares two strings (returns 0 if equal)
• strchr(str, ch) – Returns pointer to first occurrence of ch
• strstr(haystack, needle) – Returns pointer to substring

🧪 Example Program

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

int main() {
    char str1[20] = "Udaan";
    char str2[20] = "Path";
    strcat(str1, str2);  // str1 becomes "UdaanPath"
    printf("Combined: %s\n", str1);
    return 0;
}
  

📊 Real-Life Use Case – UdaanPath

Suppose you're storing user names in an educational app like UdaanPath. Each user’s name and email can be stored using strings and validated using strlen, strcmp, etc.

⚙️ Operations on Strings

• Traversing using loops
• Reversing a string
• Counting vowels, consonants, digits
• Palindrome check
• Character frequency

🧠 String vs Character Array

• A string always ends with '\0'
• Character arrays may not necessarily be null-terminated
• Use string.h functions only with null-terminated strings

📚 Practice Tasks

• Write a program to reverse a string
• Count the number of vowels and consonants
• Check if a string is a palindrome
• Compare two strings entered by user

✅ Summary

• Strings are arrays of characters ending with '\0'
• Use string.h for common operations like copy, compare, and length
• Be cautious of buffer overflow and always allocate extra space for '\0'

📤 Coming Next

In the next chapter, we’ll explore Structures and Unions — composite data types used for storing grouped and flexible data in C.