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String-Based Problems in C

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Introduction

String-based problems help improve your understanding of character arrays and string manipulation in C.

👉 These are very important for coding interviews and real-world applications.

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Why Learn String Problems?

• ✔ Improve logic building
• ✔ Master string handling
• ✔ Useful in interviews
• ✔ Strengthen problem-solving skills

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1. Find String Length (Without strlen)

#include <stdio.h>

int main() {
    char str[] = "Hello";
    int i = 0;

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

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

    return 0;
}

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Output

Length = 5

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2. Reverse a String

#include <stdio.h>

int main() {
    char str[] = "Hello";
    int i, len = 0;
    char temp;

    while (str[len] != '\0')
        len++;

    for (i = 0; i < len / 2; i++) {
        temp = str[i];
        str[i] = str[len - i - 1];
        str[len - i - 1] = temp;
    }

    printf("Reversed = %s", str);

    return 0;
}

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Output

Reversed = olleH

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3. Check Palindrome String

#include <stdio.h>

int main() {
    char str[] = "madam";
    int i, len = 0, flag = 1;

    while (str[len] != '\0')
        len++;

    for (i = 0; i < len / 2; i++) {
        if (str[i] != str[len - i - 1]) {
            flag = 0;
            break;
        }
    }

    if (flag)
        printf("Palindrome");
    else
        printf("Not Palindrome");

    return 0;
}

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Output

Palindrome

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4. Count Vowels and Consonants

#include <stdio.h>

int main() {
    char str[] = "hello";
    int i = 0, vowels = 0, consonants = 0;

    while (str[i] != '\0') {
        if (str[i]=='a'||str[i]=='e'||str[i]=='i'||str[i]=='o'||str[i]=='u')
            vowels++;
        else
            consonants++;
        i++;
    }

    printf("Vowels = %d\nConsonants = %d", vowels, consonants);

    return 0;
}

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Output

Vowels = 2
Consonants = 3

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5. Convert to Uppercase

#include <stdio.h>

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

    while (str[i] != '\0') {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = str[i] - 32;
        }
        i++;
    }

    printf("Uppercase = %s", str);

    return 0;
}

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Output

Uppercase = HELLO

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String Problems Table

Program	Purpose
Length	Find string length
Reverse	Reverse string
Palindrome	Check palindrome
Vowels	Count vowels
Uppercase	Convert case

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Important Notes

• Strings end with \0
• Use loops for processing
• Be careful with indexing

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Common Mistakes

• ❌ Missing null character
• ❌ Wrong loop conditions
• ❌ Case sensitivity issues

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Pro Tips

• ✔ Practice string problems daily
• ✔ Avoid using built-in functions initially
• ✔ Understand ASCII values
• ✔ Try different variations

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Conclusion

String-based problems are essential for mastering string manipulation in C. They improve logic and are important for interviews.

Practice regularly to become confident.

👉 This article is part of Dharani Tech Edu Hub — where learning programming is made simple and practical.