C String Functions

 C String Functions (Complete Tutorial: Beginner → Advanced)

In C String Functions are handled using character arrays and the string library
 Header file: <string.h>

C does not have a built-in string data type, so string functions are very important for real programs and interviews.

 What Is a String in C?

A string is an array of characters terminated by a null character '\0'.

Memory:

 Include String Library

 Most Common String Functions

strlen() – String Length

•  Does NOT count '\0'

strcpy() – Copy String

•  Destination must have enough space

strncpy() – Safer Copy

• Limits copy size

strcat() – Concatenate Strings

• Result → "Hello World"

strncat() – Safe Concatenation

strcmp() – Compare Strings

•  Case-sensitive

strncmp() – Compare Limited Characters

 String Search Functions

strchr() – Find Character

•  Returns pointer to first occurrence

strrchr() – Find Last Occurrence

strstr() – Find Substring

•  Output → Programming

 String Tokenization

strtok() – Split String

•  Used in CSV parsing
•  Modifies original string

 Case Conversion (Non-Standard but Common)

(For strings, loop manually)

 String Input & Output Recap

Input

Output

 Common String Mistakes

•  Forgetting '\0' 
•  Using gets() (unsafe)
•  Buffer overflow in strcpy() 
•  Comparing strings using ==

 Correct comparison:

sizeof() vs strlen()

 Important Interview Questions

1. Difference between strlen() and sizeof()

2. Why strcmp() is used instead of ==

3. Is strcpy() safe?

4. How strtok() works internally

5. What is null-terminated string?

 Real-Life Use Cases

• Input validation

• File parsing

• URL & protocol handling

• Embedded firmware

• Competitive programming

 Summary

•  Strings are character arrays
• <string.h> provides powerful utilities
•  Always handle buffer size carefully
• strcmp() for comparison, not ==
•  Extremely important for interviews & projects