String Functions in C Practice Questions with Solutions

Introduction

C provides several useful string functions through the <string.h> header file. These functions make common string operations easier, such as finding length, copying strings, comparing strings, joining strings, and searching for characters. In this chapter, you will practice the most important C string functions with simple examples. The programs also show how these functions work so beginners can understand what happens instead of simply memorizing function names. String Functions in C Practice questions with solutions to help you understand the concepts.

Q1. Find the Length of a String Using `strlen()`

Problem Statement

Write a C program to find the length of a string using the strlen() function.

C Program

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

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

    int length = strlen(name);

    printf("Length = %d", length);

    return 0;
}

Sample Output

Length = 11

Explanation

The strlen() function is used to find the number of characters in a string.

strlen(name)

For:

Programming

there are 11 characters.

The null character '\0' is not included in the returned length.

The header file is required:

#include <string.h>

Concepts Covered

strlen()
<string.h>
String length
Character arrays

Q2. Copy One String Using `strcpy()`

Problem Statement

Write a C program to copy one string into another using strcpy().

C Program

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

int main()
{
    char original[] = "C Programming";
    char copy[50];

    strcpy(copy, original);

    printf("Original: %s\n", original);
    printf("Copy: %s", copy);

    return 0;
}

Sample Output

Original: C Programming
Copy: C Programming

Explanation

The syntax of strcpy() is:

strcpy(destination, source);

In this example:

strcpy(copy, original);

means:

original → copy

The contents of original are copied into copy, including the terminating '\0'.

The destination array must have enough space to hold the copied string.

Concepts Covered

strcpy()
String copying
Source and destination
<string.h>

Q3. Compare Two Strings Using `strcmp()`

Problem Statement

Write a C program to compare two strings using strcmp().

C Program

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

int main()
{
    char first[] = "apple";
    char second[] = "apple";

    int result = strcmp(first, second);

    if (result == 0)
    {
        printf("Strings are equal.");
    }
    else
    {
        printf("Strings are not equal.");
    }

    return 0;
}

Sample Output

Strings are equal.

Explanation

The strcmp() function compares two strings.

strcmp(first, second)

Its return value is:

0       → strings are equal
&lt; 0     → first string comes before second
> 0     → first string comes after second

For example:

strcmp("apple", "apple")

returns 0.

Therefore:

if (result == 0)

is true.

Concepts Covered

strcmp()
String comparison
Return values
if-else

Q4. Join Two Strings Using `strcat()`

Problem Statement

Write a C program to join two strings using the strcat() function.

C Program

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

int main()
{
    char first[50] = "Hello ";
    char second[] = "World";

    strcat(first, second);

    printf("Result: %s", first);

    return 0;
}

Sample Output

Result: Hello World

Explanation

strcat() means string concatenation.

The syntax is:

strcat(destination, source);

Here:

strcat(first, second);

adds second to the end of first.

Before:

first  = Hello
second = World

After:

first = Hello World

The destination array must have enough unused space for the final string.

Concepts Covered

strcat()
String concatenation
Destination array
Source string

Q5. Convert a String to Lowercase Using `tolower()`

Problem Statement

Write a C program to convert uppercase letters in a string to lowercase using tolower().

C Program

#include <stdio.h>
#include <ctype.h>

int main()
{
    char text[] = "HELLO WORLD";
    int i = 0;

    while (text[i] != '\0')
    {
        text[i] = tolower((unsigned char)text[i]);
        i++;
    }

    printf("Lowercase: %s", text);

    return 0;
}

Sample Output

Lowercase: hello world

Explanation

tolower() converts an uppercase alphabetic character to lowercase.

For example:

'A' → 'a'
'B' → 'b'
'C' → 'c'

The function is provided by:

#include <ctype.h>

The loop processes each character until it reaches '\0'.

The cast:

(unsigned char)text[i]

is a safe way to pass a potentially signed char to the character-classification functions.

Concepts Covered

tolower()
<ctype.h>
String traversal
Character conversion

Q6. Convert a String to Uppercase Using `toupper()`

Problem Statement

Write a C program to convert lowercase letters in a string to uppercase using toupper().

C Program

#include <stdio.h>
#include <ctype.h>

int main()
{
    char text[] = "hello world";
    int i = 0;

    while (text[i] != '\0')
    {
        text[i] = toupper((unsigned char)text[i]);
        i++;
    }

    printf("Uppercase: %s", text);

    return 0;
}

Sample Output

Uppercase: HELLO WORLD

Explanation

The toupper() function converts a lowercase alphabetic character to uppercase.

For example:

'a' → 'A'
'b' → 'B'
'c' → 'C'

The program visits every character and converts it where applicable.

Spaces are not changed.

Concepts Covered

toupper()
<ctype.h>
String traversal
Character conversion

Q7. Find the First Occurrence of a Character Using `strchr()`

Problem Statement

Write a C program to find the first occurrence of a character in a string using strchr().

C Program

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

int main()
{
    char text[] = "programming";
    char search = 'g';

    char *result = strchr(text, search);

    if (result != NULL)
    {
        printf("Character found.");
    }
    else
    {
        printf("Character not found.");
    }

    return 0;
}

Sample Output

Character found.

Explanation

The strchr() function searches for the first occurrence of a character in a string.

Syntax:

strchr(string, character);

Here:

strchr(text, search);

searches for:

'g'

inside:

programming

If the character is found, strchr() returns a pointer to its location.

If it is not found, it returns:

NULL

Concepts Covered

strchr()
Character searching
Pointers
NULL
<string.h>

Q8. Find a Substring Using `strstr()`

Problem Statement

Write a C program to check whether a particular word or substring exists inside another string using strstr().

C Program

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

int main()
{
    char text[] = "I am learning C programming.";
    char search[] = "C programming";

    char *result = strstr(text, search);

    if (result != NULL)
    {
        printf("Substring found.");
    }
    else
    {
        printf("Substring not found.");
    }

    return 0;
}

Sample Output

Substring found.

Explanation

strstr() searches for one string inside another string.

Syntax:

strstr(main_string, search_string);

Here:

strstr(text, search);

searches for:

C programming

inside:

I am learning C programming.

If the substring exists, the function returns a pointer to its first character.

If it doesn’t exist, it returns NULL.

Concepts Covered

strstr()
Substring searching
Pointers
NULL

Q9. Read a Full Sentence and Find Its Length

Problem Statement

Write a C program that takes a sentence from the user and finds its length using strlen().

C Program

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

int main()
{
    char sentence[100];

    printf("Enter a sentence: ");
    fgets(sentence, sizeof(sentence), stdin);

    sentence[strcspn(sentence, "\n")] = '\0';

    printf("Length = %zu", strlen(sentence));

    return 0;
}

Sample Output

Enter a sentence: I love C programming
Length = 20

Explanation

We use:

fgets(sentence, sizeof(sentence), stdin);

because the sentence may contain spaces.

When fgets() reads a line, it can also store the newline character '\n' if there is room.

This line removes that newline:

sentence[strcspn(sentence, "\n")] = '\0';

Then:

strlen(sentence)

returns the number of characters in the sentence, excluding the terminating '\0'.

Notice that strlen() returns a size_t, so %zu is the appropriate printf() format specifier.

Concepts Covered

fgets()
strlen()
strcspn()
Strings with spaces
size_t

Q10. Create a Small Student Name Program Using Multiple String Functions

Problem Statement

Write a C program that takes a student’s first name and last name, joins them, and displays the complete name and its length.

C Program

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

int main()
{
    char firstName[50];
    char lastName[50];
    char fullName[100];

    printf("Enter first name: ");
    scanf("%49s", firstName);

    printf("Enter last name: ");
    scanf("%49s", lastName);

    strcpy(fullName, firstName);
    strcat(fullName, " ");
    strcat(fullName, lastName);

    printf("\nFull Name: %s\n", fullName);
    printf("Name Length: %zu", strlen(fullName));

    return 0;
}

Sample Output

Enter first name: Rahul
Enter last name: Kumar

Full Name: Rahul Kumar
Name Length: 11

Explanation

This program combines multiple string functions.

First, the first name is copied into fullName:

strcpy(fullName, firstName);

Then a space is added:

strcat(fullName, " ");

Finally, the last name is added:

strcat(fullName, lastName);

The final string becomes:

Rahul Kumar

Then strlen() calculates its length.

The program demonstrates how different string functions can be combined to solve a practical problem.

Concepts Covered

strcpy()
strcat()
strlen()
Multiple string operations
Practical string handling

Key Takeaways

String functions make common string operations easier in C.
Most C string functions are available through <string.h>.
strlen() finds the number of characters in a string.
strcpy() copies one string into another.
strcmp() compares two strings.
strcat() joins one string to another.
strchr() searches for a character.
strstr() searches for a substring.
strcspn() can help remove the newline read by fgets().
toupper() and tolower() are available through <ctype.h>.
String destination arrays must have enough space when using copying or concatenation functions.
strcmp() returns 0 when two strings are equal.
Understanding manual string operations is useful even when using library functions.
Always remember that a C string ends with '\0'.

FAQs

1. Which header file is used for C string functions?

Most standard C string functions are declared in:

#include <string.h>

2. What does `strlen()` do in C?

strlen() returns the number of characters in a string, excluding the terminating '\0'.

Example:

strlen("Hello")

returns 5.

3. What is the difference between `strcpy()` and `strcat()`?

strcpy() copies a string:

strcpy(destination, source);

strcat() appends one string to another:

strcat(destination, source);

4. How do you compare two strings in C?

Use strcmp():

if (strcmp(first, second) == 0)
{
    printf("Equal");
}

5. What does `strcmp()` return when strings are equal?

It returns 0 when the two strings are equal.

6. What is the difference between `strchr()` and `strstr()`?

strchr() searches for a single character.

strchr(text, 'a');

strstr() searches for a string or substring.

strstr(text, "program");

7. Why does `strcat()` require enough space in the destination array?

strcat() adds the source string to the destination string. The destination must have enough available space for the original contents, appended contents, and terminating '\0'. It does not automatically allocate additional memory.

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar

Introduction

Q1. Find the Length of a String Using strlen()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q2. Copy One String Using strcpy()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q3. Compare Two Strings Using strcmp()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q4. Join Two Strings Using strcat()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q5. Convert a String to Lowercase Using tolower()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q6. Convert a String to Uppercase Using toupper()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q7. Find the First Occurrence of a Character Using strchr()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q8. Find a Substring Using strstr()

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q9. Read a Full Sentence and Find Its Length

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Q10. Create a Small Student Name Program Using Multiple String Functions

Problem Statement

C Program

Sample Output

Explanation

Concepts Covered

Key Takeaways

FAQs

1. Which header file is used for C string functions?

2. What does strlen() do in C?

3. What is the difference between strcpy() and strcat()?

4. How do you compare two strings in C?

5. What does strcmp() return when strings are equal?

6. What is the difference between strchr() and strstr()?

7. Why does strcat() require enough space in the destination array?

Related Posts

Q1. Find the Length of a String Using `strlen()`

Q2. Copy One String Using `strcpy()`

Q3. Compare Two Strings Using `strcmp()`

Q4. Join Two Strings Using `strcat()`

Q5. Convert a String to Lowercase Using `tolower()`

Q6. Convert a String to Uppercase Using `toupper()`

Q7. Find the First Occurrence of a Character Using `strchr()`

Q8. Find a Substring Using `strstr()`

2. What does `strlen()` do in C?

3. What is the difference between `strcpy()` and `strcat()`?

5. What does `strcmp()` return when strings are equal?

6. What is the difference between `strchr()` and `strstr()`?

7. Why does `strcat()` require enough space in the destination array?