Strings in C

So far, you've learned how to store numbers using variables and arrays. But what if you need to store text such as a person's name, email address, city, or password?

Instead of storing each character separately, C provides strings, which allow us to store and manipulate text efficiently.

A string is one of the most frequently used data types in programming. Applications like chat systems, login forms, search engines, compilers, and databases all rely heavily on strings.

🎯 Learning Objectives

After completing this lesson, you will be able to:

• Understand what strings are.
• Learn how strings are stored in memory.
• Declare and initialize strings.
• Read and print strings.
• Use common string functions.
• Compare, copy, and concatenate strings.
• Avoid common mistakes while working with strings.

📖 What is a String?

A string is a sequence of characters terminated by a special character called the null character ('\0').

Unlike integers and floating-point numbers, strings are stored as arrays of characters.

Example

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char name[] = "KauraX";

Memory representation:

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+---+---+---+---+---+---+----+
| K | a | u | r | a | X | \0 |
+---+---+---+---+---+---+----+

The null character marks the end of the string.

Why is the Null Character Important?

The C compiler doesn't know where a string ends unless it encounters '\0'.

Example

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char name[] = "Hi";

Memory:

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Index : 0   1   2

Value : H   i  \0

Without the null character, functions like printf() would continue reading memory beyond the string, leading to undefined behavior.

Declaring Strings

Method 1

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char name[20];

Allocates space for 20 characters.

Method 2

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char name[] = "KauraX";

The compiler automatically determines the size.

Method 3

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char name[] = {'K','a','u','r','a','X','\0'};

Equivalent to the previous declaration.

Reading Strings

Using scanf()

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#include <stdio.h>

int main()
{
    char name[30];

    printf("Enter your name: ");
    scanf("%s", name);

    printf("Hello %s", name);

    return 0;
}

Output

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Enter your name: KauraX
Hello KauraX

Reading Strings with Spaces

Use fgets() instead.

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#include <stdio.h>

int main()
{
    char name[50];

    printf("Enter Full Name: ");

    fgets(name, sizeof(name), stdin);

    printf("%s", name);

    return 0;
}

Printing Strings

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printf("%s", name);

The %s format specifier is used for strings.

Accessing Individual Characters

Since strings are arrays, each character has an index.

Example

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char course[] = "KauraX";

printf("%c", course[0]);

Output

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K

Modifying Characters

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char name[] = "KauraX";

name[0] = 'k';

printf("%s", name);

Output

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kauraX

Standard String Library

To use string functions, include:

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#include <string.h>

strlen()

Returns the length of a string (excluding '\0').

Example

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

int main()
{
    char name[] = "KauraX";

    printf("%lu", strlen(name));

    return 0;
}

Output

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6

strcpy()

Copies one string into another.

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

int main()
{
    char source[] = "KauraX";
    char destination[20];

    strcpy(destination, source);

    printf("%s", destination);

    return 0;
}

Output

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KauraX

strcat()

Appends one string to another.

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

int main()
{
    char first[30] = "Hello ";

    strcat(first, "KauraX");

    printf("%s", first);

    return 0;
}

Output

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Hello KauraX

strcmp()

Compares two strings.

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

int main()
{
    char a[] = "Apple";
    char b[] = "Apple";

    printf("%d", strcmp(a, b));

    return 0;
}

Output

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0

Meaning:

• 0 → Equal
• < 0 → First string is smaller
• > 0 → First string is greater

Common String Operations

Reverse a String

Example logic:

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Input:
KauraX

Output:
XaruaK

Count Vowels

Input

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Programming

Output

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Vowels = 3

Count Characters

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strlen(name)

Check Palindrome

Example

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madam

Output

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Palindrome

String vs Character Array

Real-World Example

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#include <stdio.h>

int main()
{
    char student[] = "Pritee";

    printf("Welcome to KauraX\n");

    printf("Student : %s", student);

    return 0;
}

Output

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Welcome to KauraX
Student : Pritee

Common Beginner Mistakes

Forgetting Space for Null Character

Wrong

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char name[5] = "Hello";

Correct

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char name[6] = "Hello";

Using == for String Comparison

Wrong

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if(name == anotherName)

Correct

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if(strcmp(name, anotherName) == 0)

Using gets()

Avoid

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gets(name);

It is unsafe and has been removed from the C standard.

Use

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fgets()

instead.

Best Practices

• Always allocate enough memory for the null character.
• Use fgets() instead of gets().
• Use strcmp() for comparison.
• Include <string.h> when using string functions.
• Validate user input whenever possible.

🧠 Interview Questions

1. What is a string in C?
2. Why is the null character important?
3. Differentiate between a character and a string.
4. Explain strlen().
5. Explain strcpy().
6. Explain strcmp().
7. Explain strcat().
8. Why is gets() unsafe?

✍ Practice Questions

1. Read and print a string.
2. Find the length of a string.
3. Reverse a string.
4. Count vowels and consonants.
5. Check whether a string is a palindrome.
6. Compare two strings.
7. Copy one string into another.
8. Concatenate two strings.
9. Count words in a sentence.
10. Convert lowercase letters to uppercase.

📚 Lesson Summary

In this lesson, you learned:

• What strings are.
• How strings are stored in memory.
• Declaring and initializing strings.
• Reading and printing strings.
• Standard string functions (strlen(), strcpy(), strcat(), strcmp()).
• Common mistakes and best practices.

Strings are one of the most important concepts in C because almost every application processes text in some form. Mastering strings is essential before learning pointers and advanced data structures.

🚀 What's Next?

In the next lesson, Pointers in C, you'll learn:

• Memory addresses
• Pointer declaration
• Pointer arithmetic
• Pointers and arrays
• Pointers and functions
• Dynamic memory basics
• Practical examples
• Interview questions

Pointers are one of the most powerful and challenging concepts in C, enabling efficient memory management and advanced programming techniques.

Happy Coding with KauraX 💙