🌟 The Honest Journey of a Student: Learning, Failing, and Growing

📘 C Programming Practice Programs

📚 Covers: Operators | Decision Making | Loops | Nested Loops | Break | Continue

✍ Written by Krishna Popat

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🚀 Introduction

After completing the basics of C programming, students must practice logic-based programs to strengthen their understanding.

This blog contains 10 moderate to hard level C programs.
Each program includes:

• Understanding before the code

• Comment on every single line of code

• Output after execution

This makes it perfect for lab submission, exams, and blogging.

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✅ PROGRAM 1: ARMSTRONG NUMBER CHECK

🔍 Understanding

An Armstrong number is a number whose sum of the cubes of its digits equals the number itself.
Example: 153 = 1³ + 5³ + 3³

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#include <stdio.h>                 // Include standard input-output header file

int main()                         // Main function starts program execution
{
    int num;                       // Variable to store the input number
    int originalNum;               // Variable to store the original number
    int digit;                     // Variable to store each extracted digit
    int sum = 0;                   // Variable to store sum of cubes of digits

    printf("Enter a number: ");    // Prompt user to enter a number
    scanf("%d", &num);             // Read number from user

    originalNum = num;             // Store original number for comparison

    while(num > 0)                 // Loop until number becomes zero
    {
        digit = num % 10;          // Extract the last digit
        sum = sum + digit*digit*digit; // Add cube of digit to sum
        num = num / 10;            // Remove last digit from number
    }

    if(sum == originalNum)         // Check Armstrong condition
        printf("Armstrong Number"); // Print if condition is true
    else
        printf("Not an Armstrong Number"); // Print if condition is false

    return 0;                      // End of program
}

🖥 Output

Enter a number: 153
Armstrong Number

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✅ PROGRAM 2: PERFECT NUMBER CHECK

🔍 Understanding

A perfect number is a number whose sum of its proper divisors equals the number itself.
Example: 6 = 1 + 2 + 3

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#include <stdio.h>                 // Include input-output header

int main()                         // Main function
{
    int num;                       // Variable to store the number
    int i;                         // Loop counter variable
    int sum = 0;                   // Variable to store sum of divisors

    printf("Enter a number: ");    // Ask user for input
    scanf("%d", &num);             // Read the number

    for(i = 1; i <= num/2; i++)    // Loop from 1 to half of number
    {
        if(num % i == 0)           // Check if i is a divisor
            sum = sum + i;         // Add divisor to sum
    }

    if(sum == num)                 // Check perfect number condition
        printf("Perfect Number");  // Print if true
    else
        printf("Not a Perfect Number"); // Print if false

    return 0;                      // End program
}

🖥 Output

Enter a number: 6
Perfect Number

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✅ PROGRAM 3: PRIME NUMBERS BETWEEN TWO NUMBERS

🔍 Understanding

This program prints prime numbers in a given range using nested loops, break, and continue.

---

#include <stdio.h>                     // Include input-output library

int main()                             // Main function
{
    int start, end;                    // Variables to store range
    int i, j;                          // Loop counters
    int isPrime;                       // Flag variable for prime check

    printf("Enter start and end: ");   // Ask user for range
    scanf("%d %d", &start, &end);      // Read range values

    for(i = start; i <= end; i++)      // Outer loop through range
    {
        if(i <= 1)                     // Check for invalid numbers
            continue;                  // Skip to next iteration

        isPrime = 1;                   // Assume number is prime

        for(j = 2; j <= i/2; j++)      // Inner loop for divisibility check
        {
            if(i % j == 0)             // If divisible
            {
                isPrime = 0;           // Mark as not prime
                break;                 // Exit inner loop
            }
        }

        if(isPrime == 1)               // If number is prime
            printf("%d ", i);          // Print the prime number
    }

    return 0;                          // End program
}

🖥 Output

Enter start and end: 10 20
11 13 17 19

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✅ PROGRAM 4: HCF (GCD) OF TWO NUMBERS

🔍 Understanding

HCF is the greatest number that divides both numbers exactly.

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#include <stdio.h>                 // Include standard library

int main()                         // Main function
{
    int a, b;                      // Variables for two numbers
    int i;                         // Loop counter
    int hcf = 1;                   // Variable to store HCF

    printf("Enter two numbers: "); // Ask user for input
    scanf("%d %d", &a, &b);        // Read both numbers

    for(i = 1; i <= a && i <= b; i++) // Loop till smaller number
    {
        if(a % i == 0 && b % i == 0)  // Check common divisor
            hcf = i;               // Store divisor
    }

    printf("HCF = %d", hcf);       // Print HCF

    return 0;                      // End program
}

🖥 Output

Enter two numbers: 12 18
HCF = 6

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✅ PROGRAM 5: DECIMAL TO BINARY (NO ARRAY)

🔍 Understanding

Binary number is formed by dividing the decimal number by 2 repeatedly and storing remainders.

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#include <stdio.h>                 // Include input-output library

int main()                         // Main function
{
    int num;                       // Variable to store decimal number
    int binary = 0;                // Variable to store binary result
    int place = 1;                 // Variable to store place value
    int remainder;                 // Variable to store remainder

    printf("Enter decimal number: "); // Ask user input
    scanf("%d", &num);             // Read decimal number

    while(num > 0)                 // Loop until number becomes zero
    {
        remainder = num % 2;       // Get remainder
        binary = binary + remainder * place; // Build binary number
        place = place * 10;        // Increase place value
        num = num / 2;             // Divide number by 2
    }

    printf("Binary = %d", binary); // Print binary number

    return 0;                      // End program
}

🖥 Output

Enter decimal number: 13
Binary = 1101


✅ PROGRAM 6: REVERSE NUMBER & PALINDROME CHECK
🔍 Understanding
A palindrome number remains the same when reversed.

Example: 121 → 121 (Palindrome), 123 → 321 (Not Palindrome)

Logic:
Extract digits using % 10
Build reverse using multiplication by 10
Compare reversed number with original

#include <stdio.h>                    // Include input-output library

int main()                            // Main function
{
    int num;                          // Variable to store input number
    int originalNum;                  // Variable to store original number
    int reverse = 0;                  // Variable to store reversed number
    int digit;                        // Variable to store extracted digit

    printf("Enter a number: ");       // Ask user for input
    scanf("%d", &num);                // Read number from user

    originalNum = num;                // Store original number

    while(num > 0)                    // Loop until number becomes zero
    {
        digit = num % 10;             // Extract last digit
        reverse = reverse * 10 + digit; // Build reversed number
        num = num / 10;               // Remove last digit
    }

    if(reverse == originalNum)        // Compare reversed and original
        printf("Palindrome Number");  // If same
    else
        printf("Not a Palindrome Number"); // If different

    return 0;                         // End program
}

🖥 Output
Enter a number: 121
Palindrome Number


✅ PROGRAM 7: FLOYD’S TRIANGLE (Nested Loops)
🔍 Understanding
Floyd’s Triangle prints consecutive numbers in triangle form using nested loops.

#include <stdio.h>                    // Include standard library

int main()                            // Main function
{
    int rows;                         // Variable to store number of rows
    int i, j;                         // Loop counters
    int num = 1;                      // Variable to print numbers

    printf("Enter number of rows: "); // Ask user input
    scanf("%d", &rows);               // Read rows

    for(i = 1; i <= rows; i++)        // Outer loop for rows
    {
        for(j = 1; j <= i; j++)       // Inner loop for columns
        {
            printf("%d ", num);       // Print current number
            num++;                    // Increment number
        }
        printf("\n");                 // Move to next line
    }

    return 0;                         // End program
}

🖥 Output
1
2 3
4 5 6
7 8 9 10


✅ PROGRAM 8: FREQUENCY OF EACH DIGIT IN A NUMBER
🔍 Understanding
This program counts how many times each digit (0–9) appears in a number.

#include <stdio.h>                     // Include input-output library

int main()                             // Main function
{
    int num;                           // Variable to store number
    int temp;                          // Temporary copy of number
    int digit;                         // Variable to store extracted digit
    int i;                             // Loop variable for digits 0–9
    int count;                         // Counter variable

    printf("Enter a number: ");        // Ask user input
    scanf("%d", &num);                 // Read number

    for(i = 0; i <= 9; i++)            // Loop for digits 0 to 9
    {
        temp = num;                    // Copy original number
        count = 0;                     // Reset count

        while(temp > 0)                // Loop through digits
        {
            digit = temp % 10;         // Extract digit
            if(digit == i)             // Compare digit
                count++;               // Increase count
            temp = temp / 10;          // Remove digit
        }

        if(count > 0)                  // Print only if digit exists
            printf("Digit %d occurs %d times\n", i, count);
    }

    return 0;                          // End program
}

🖥 Output
Enter a number: 122333
Digit 1 occurs 1 times
Digit 2 occurs 2 times
Digit 3 occurs 3 times


✅ PROGRAM 9: HARMONIC SERIES
🔍 Understanding
Calculates the sum:

1 + 1/2 + 1/3 + ... + 1/n

#include <stdio.h>                    // Include standard library

int main()                            // Main function
{
    int n;                            // Variable for number of terms
    int i;                            // Loop variable
    float sum = 0.0;                  // Variable to store sum

    printf("Enter value of n: ");     // Ask user input
    scanf("%d", &n);                  // Read n

    for(i = 1; i <= n; i++)           // Loop from 1 to n
    {
        sum = sum + (1.0 / i);        // Add term to sum
    }

    printf("Sum = %.2f", sum);        // Print result

    return 0;                         // End program
}

🖥 Output
Enter value of n: 5
Sum = 2.28


✅ PROGRAM 10: MENU-DRIVEN CALCULATOR (Switch + Break)
🔍 Understanding
Performs arithmetic operations based on user choice using switch.

#include <stdio.h>                       // Include input-output library

int main()                               // Main function
{
    int choice;                          // Variable for menu choice
    float a, b;                          // Variables for numbers

    printf("1. Add\n");                 // Menu option
    printf("2. Subtract\n");
    printf("3. Multiply\n");
    printf("4. Divide\n");

    printf("Enter your choice: ");      // Ask user choice
    scanf("%d", &choice);               // Read choice

    printf("Enter two numbers: ");      // Ask for numbers
    scanf("%f %f", &a, &b);             // Read numbers

    switch(choice)                      // Switch statement
    {
        case 1:                         // Addition case
            printf("Result = %.2f", a + b);
            break;

        case 2:                         // Subtraction case
            printf("Result = %.2f", a - b);
            break;

        case 3:                         // Multiplication case
            printf("Result = %.2f", a * b);
            break;

        case 4:                         // Division case
            if(b != 0)
                printf("Result = %.2f", a / b);
            else
                printf("Division by zero not allowed");
            break;

        default:                        // Invalid choice
            printf("Invalid choice");
    }

    return 0;                           // End program
}

🖥 Output
Enter your choice: 1
Enter two numbers: 10 5
Result = 15.00
🎯 FINAL ACADEMIC CONCLUSION

After completing these 10 structured programs:
✔ Loop concepts are strong

✔ Nested loop logic is clear

✔ Decision-making is confident

✔ Break & Continue are understood

✔ Logical thinking is improved

This collection represents a complete moderate-to-hard practice set suitable for:
Laboratory submission
University internal assessment
Exam preparation
Strong foundation for Functions in C


📘 Part of the C Programming Beginner Series
🌐 Blog: LEARNING GROWTH HUB
✍️ Author: Krishna Popat