C Programming Practice Set 6 – Strings

Strings are one of the most commonly used data types in C. They are simply arrays of characters terminated by a null character ('\0'). Understanding string manipulation is essential for file handling, text processing, and many real-world applications.

In this practice set, you'll solve common string-based problems using both library functions and manual implementations.

Each program includes:

🎯 Objective
💡 Problem Statement
💻 C Program
▶ Sample Input
✅ Sample Output
📚 Explanation

Program 1 — Read and Display a String

🎯 Objective

Learn how to input and print strings.

Program

c
#include <stdio.h>

int main()
{
    char str[100];

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

    printf("You entered: %s", str);

    return 0;
}

Program 2 — Find String Length (Without strlen)

c
#include <stdio.h>

int main()
{
    char str[100];
    int length = 0;

    fgets(str, sizeof(str), stdin);

    while(str[length] != '\0' && str[length] != '\n')
    {
        length++;
    }

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

    return 0;
}

Program 3 — Copy a String (Without strcpy)

c
#include <stdio.h>

int main()
{
    char source[100];
    char destination[100];
    int i = 0;

    fgets(source, sizeof(source), stdin);

    while(source[i] != '\0')
    {
        destination[i] = source[i];
        i++;
    }

    destination[i] = '\0';

    printf("%s", destination);

    return 0;
}

Program 4 — Concatenate Two Strings (Without strcat)

c
#include <stdio.h>

int main()
{
    char first[100], second[100];
    int i = 0, j = 0;

    fgets(first, sizeof(first), stdin);
    fgets(second, sizeof(second), stdin);

    while(first[i] != '\0')
    {
        i++;
    }

    if(i > 0 && first[i - 1] == '\n')
    {
        i--;
    }

    while(second[j] != '\0')
    {
        first[i++] = second[j++];
    }

    first[i] = '\0';

    printf("%s", first);

    return 0;
}

Program 5 — Reverse a String

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

int main()
{
    char str[100];
    int length;

    fgets(str, sizeof(str), stdin);

    length = strlen(str);

    if(str[length - 1] == '\n')
    {
        str[--length] = '\0';
    }

    for(int i = length - 1; i >= 0; i--)
    {
        printf("%c", str[i]);
    }

    return 0;
}

Program 6 — Check Palindrome String

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

int main()
{
    char str[100];
    int left = 0;

    fgets(str, sizeof(str), stdin);

    int right = strlen(str);

    if(str[right - 1] == '\n')
        right--;

    right--;

    while(left < right)
    {
        if(str[left] != str[right])
        {
            printf("Not Palindrome");
            return 0;
        }

        left++;
        right--;
    }

    printf("Palindrome");

    return 0;
}

Program 7 — Count Vowels, Consonants, Digits and Spaces

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

int main()
{
    char str[200];
    int vowels = 0, consonants = 0, digits = 0, spaces = 0;

    fgets(str, sizeof(str), stdin);

    for(int i = 0; str[i] != '\0'; i++)
    {
        char ch = tolower(str[i]);

        if(ch=='a'||ch=='e'||ch=='i'||ch=='o'||ch=='u')
            vowels++;
        else if(isalpha(ch))
            consonants++;
        else if(isdigit(ch))
            digits++;
        else if(ch==' ')
            spaces++;
    }

    printf("Vowels = %d\n", vowels);
    printf("Consonants = %d\n", consonants);
    printf("Digits = %d\n", digits);
    printf("Spaces = %d\n", spaces);

    return 0;
}

Program 8 — Compare Two Strings (Without strcmp)

c
#include <stdio.h>

int main()
{
    char first[100], second[100];
    int i = 0;

    fgets(first, sizeof(first), stdin);
    fgets(second, sizeof(second), stdin);

    while(first[i] == second[i] &&
          first[i] != '\0' &&
          second[i] != '\0')
    {
        i++;
    }

    if(first[i] == second[i])
        printf("Strings are Equal");
    else
        printf("Strings are Not Equal");

    return 0;
}

Program 9 — Convert String to Uppercase

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

int main()
{
    char str[100];

    fgets(str, sizeof(str), stdin);

    for(int i = 0; str[i] != '\0'; i++)
    {
        str[i] = toupper(str[i]);
    }

    printf("%s", str);

    return 0;
}

Program 10 — Convert String to Lowercase

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

int main()
{
    char str[100];

    fgets(str, sizeof(str), stdin);

    for(int i = 0; str[i] != '\0'; i++)
    {
        str[i] = tolower(str[i]);
    }

    printf("%s", str);

    return 0;
}

⭐ Practice Challenge

Try solving these problems on your own.

Count the frequency of each character.
Remove all spaces from a string.
Count the number of words.
Replace vowels with *.
Find the first non-repeating character.
Find the first repeating character.
Sort characters alphabetically.
Check whether two strings are anagrams.
Remove duplicate characters.
Find the longest word in a sentence.

📚 Summary

In this practice set, you learned:

Reading strings
Finding string length
Copying strings
Concatenating strings
Reversing strings
Palindrome checking
Counting vowels, consonants, digits, and spaces
Comparing strings
Converting strings to uppercase and lowercase

These operations form the foundation of text processing and are widely used in file handling, compilers, and software applications.

🚀 What's Next?

In Practice Set 7 – Pointers, you'll solve problems involving:

Pointer basics
Pointer arithmetic
Swapping using pointers
Arrays and pointers
Strings using pointers
Dynamic memory allocation
Pointer to pointer
Function pointers (Introduction)

Happy Coding with KauraX 💙

Practice Set 6 – Strings