Age in Days: Ask the user to enter their age in years, then calculate and print roughly how many days old they are (age * 365).

Rectangle Perimeter & Area: Prompt for the length and width of a room as integers. Output both its perimeter ($2 \times (l + w)$) and area ($l \times w$).

Candy Splitter: Enter total candies and the number of friends. Use / to show how many each person gets, and % (modulus) to display how many are left over.

Time Converter: Ask for a total number of minutes (e.g., 145) and convert it into hours and remaining minutes (e.g., "2 hours and 25 minutes").

Split the Dinner Bill: Enter the total restaurant bill and number of diners. Calculate and print each person’s share formatted to two decimal places.

Temperature Converter: Take a temperature in Celsius as a float and convert it to Fahrenheit using $F = (C \times 9.0 / 5.0) + 32.0$.

Circle Calculator: Input the radius of a circle as a float. Compute and display both the circumference ($2 \times 3.14159 \times r$) and area ($3.14159 \times r^2$).

Simple Interest: Ask for principal amount, annual interest rate (e.g., 5.5%), and time in years. Calculate simple interest: $(P \times R \times T) / 100$.

1. Secret ASCII Decoder: Input a single character and print both the character and its hidden numerical ASCII value (%d).
2. Case Switcher: Take a lowercase character (like 'a') and convert it to uppercase ('A') by subtracting 32 from its ASCII code.
3. Next in Line: Read a letter from the keyboard and print the letter that immediately follows it in the alphabet (e.g., 'b' follows 'a').
4. Vowel or Consonant: Read one lowercase letter and use a simple if-else statement to determine whether it is a vowel (a, e, i, o, u) or a consonant.

Greeting Generator: Take a user's first name as a string and print a custom banner message: *** Welcome, [Name]! ***.

Character Count (No Library): Input a word and write a while loop that counts how many letters it contains until it encounters the null terminator '\0'.

Initials Extractor: Read a first name and last name as two separate strings, then print the user's initials (e.g., "John Doe" $\rightarrow$ "J.D.").

Reverse a Word: Enter a short word (like "code") and print it backward letter-by-letter ("edoc").

Supermarket Receipt: Ask for an item code (char), quantity (int), and price per unit (float). Print a formatted receipt line showing the total cost.

Student Grade Card: Input a student's name (string), roll number (int), and three exam scores (float). Print their details along with their final average percentage.

Digit Sum Extractor: Take a 3-digit integer (e.g., 456), extract each digit using / and %, and calculate their sum ($4 + 5 + 6 = 15$).

Mini ATM Simulator: Set a starting bank balance as a float. Prompt the user to deposit or withdraw an amount, check if funds are sufficient, and display the updated balance.

1. Age in Days

C

#include <stdio.h>

int main() {
    int age, days;

    printf("Enter your age in years: ");
    scanf("%d", &age);

    days = age * 365;

    printf("You are approximately %d days old!\n", days);
    return 0;
}

2. Rectangle Perimeter & Area

C

#include <stdio.h>

int main() {
    int length, width;

    printf("Enter length and width: ");
    scanf("%d %d", &length, &width);

    int perimeter = 2 * (length + width);
    int area = length * width;

    printf("Perimeter: %d\n", perimeter);
    printf("Area: %d\n", area);
    return 0;
}

3. Candy Splitter

C

#include <stdio.h>

int main() {
    int candies, friends;

    printf("Enter total candies: ");
    scanf("%d", &candies);
    printf("Enter number of friends: ");
    scanf("%d", &friends);

    int each = candies / friends;
    int leftover = candies % friends;

    printf("Each friend gets: %d candies\n", each);
    printf("Leftover candies: %d\n", leftover);
    return 0;
}

4. Time Converter

C

#include <stdio.h>

int main() {
    int total_minutes;

    printf("Enter total minutes: ");
    scanf("%d", &total_minutes);

    int hours = total_minutes / 60;
    int minutes = total_minutes % 60;

    printf("%d minutes = %d hour(s) and %d minute(s)\n", total_minutes, hours, minutes);
    return 0;
}

Level 2: Floating-Point Math (float, %.2f)

5. Split the Dinner Bill

C

#include <stdio.h>

int main() {
    float bill;
    int people;

    printf("Enter total bill amount: ");
    scanf("%f", &bill);
    printf("Enter number of people: ");
    scanf("%d", &people);

    float share = bill / people;

    printf("Each person pays: $%.2f\n", share);
    return 0;
}

6. Temperature Converter

C

#include <stdio.h>

int main() {
    float celsius, fahrenheit;

    printf("Enter temperature in Celsius: ");
    scanf("%f", &celsius);

    fahrenheit = (celsius * 9.0 / 5.0) + 32.0;

    printf("%.2f C is equal to %.2f F\n", celsius, fahrenheit);
    return 0;
}

7. Circle Calculator

C

#include <stdio.h>

int main() {
    float radius;
    const float PI = 3.14159;

    printf("Enter radius of the circle: ");
    scanf("%f", &radius);

    float circumference = 2 * PI * radius;
    float area = PI * radius * radius;

    printf("Circumference: %.2f\n", circumference);
    printf("Area: %.2f\n", area);
    return 0;
}

8. Simple Interest

C

#include <stdio.h>

int main() {
    float principal, rate, time;

    printf("Enter Principal, Rate (%%), and Time (years): ");
    scanf("%f %f %f", &principal, &rate, &time);

    float interest = (principal * rate * time) / 100.0;

    printf("Simple Interest earned: %.2f\n", interest);
    printf("Total Amount: %.2f\n", principal + interest);
    return 0;
}

Level 3: Characters & ASCII Codes (char, %c)

9. Secret ASCII Decoder

C

#include <stdio.h>

int main() {
    char ch;

    printf("Enter any character: ");
    scanf(" %c", &ch); // Leading space avoids reading leftover newlines

    printf("Character: '%c'\n", ch);
    printf("ASCII Value: %d\n", ch);
    return 0;
}

10. Case Switcher

C

#include <stdio.h>

int main() {
    char lower;

    printf("Enter a lowercase letter: ");
    scanf(" %c", &lower);

    // In ASCII, uppercase letters are 32 positions before lowercase
    char upper = lower - 32;

    printf("Uppercase: %c\n", upper);
    return 0;
}

11. Next in Line

C

#include <stdio.h>

int main() {
    char ch;

    printf("Enter a letter: ");
    scanf(" %c", &ch);

    char next = ch + 1;

    printf("The next letter is: %c\n", next);
    return 0;
}

12. Vowel or Consonant

C

#include <stdio.h>

int main() {
    char ch;

    printf("Enter a lowercase letter: ");
    scanf(" %c", &ch);

    if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
        printf("'%c' is a vowel.\n", ch);
    } else {
        printf("'%c' is a consonant.\n", ch);
    }
    return 0;
}

Level 4: Strings & Word Play (char[], %s)

13. Greeting Generator

C

#include <stdio.h>

int main() {
    char name[50];

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

    printf("*******************************\n");
    printf("   Welcome to Coding, %s!      \n", name);
    printf("*******************************\n");
    return 0;
}

14. Character Count (No Library)

C

#include <stdio.h>

int main() {
    char word[100];
    int count = 0;

    printf("Enter a single word: ");
    scanf("%s", word);

    // Loop until we reach the null character '\0'
    while (word[count] != '\0') {
        count++;
    }

    printf("The word \"%s\" has %d characters.\n", word, count);
    return 0;
}

15. Initials Extractor

C

#include <stdio.h>

int main() {
    char first[50], last[50];

    printf("Enter first and last name: ");
    scanf("%s %s", first, last);

    // The first character of each string is at index 0
    printf("Initials: %c.%c.\n", first[0], last[0]);
    return 0;
}

16. Reverse a Word

C

#include <stdio.h>

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

    printf("Enter a word to reverse: ");
    scanf("%s", word);

    // 1. Find the length
    while (word[length] != '\0') {
        length++;
    }

    // 2. Print backwards starting from the last valid character
    printf("Reversed: ");
    for (int i = length - 1; i >= 0; i--) {
        printf("%c", word[i]);
    }
    printf("\n");

    return 0;
}

Level 5: Mixed Types & Mini-Projects

17. Supermarket Receipt

C

#include <stdio.h>

int main() {
    char item_code;
    int qty;
    float unit_price;

    printf("Enter Item Code (single character): ");
    scanf(" %c", &item_code);

    printf("Enter Quantity: ");
    scanf("%d", &qty);

    printf("Enter Unit Price: ");
    scanf("%f", &unit_price);

    float total = qty * unit_price;

    printf("\n--- STORE RECEIPT ---\n");
    printf("Item Code : %c\n", item_code);
    printf("Quantity  : %d\n", qty);
    printf("Unit Price: $%.2f\n", unit_price);
    printf("Total Due : $%.2f\n", total);
    printf("---------------------\n");

    return 0;
}

18. Student Grade Card

C

#include <stdio.h>

int main() {
    char name[50];
    int roll_no;
    float m1, m2, m3;

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

    printf("Enter roll number: ");
    scanf("%d", &roll_no);

    printf("Enter 3 subject marks (out of 100): ");
    scanf("%f %f %f", &m1, &m2, &m3);

    float average = (m1 + m2 + m3) / 3.0;

    printf("\n--- REPORT CARD ---\n");
    printf("Name    : %s\n", name);
    printf("Roll No : %d\n", roll_no);
    printf("Average : %.2f%%\n", average);
    return 0;
}

19. Digit Sum Extractor

C

#include <stdio.h>

int main() {
    int num;

    printf("Enter a 3-digit number (e.g., 456): ");
    scanf("%d", &num);

    int d3 = num % 10;        // Last digit (6)
    int d2 = (num / 10) % 10; // Middle digit (5)
    int d1 = num / 100;       // First digit (4)

    int sum = d1 + d2 + d3;

    printf("Digits: %d + %d + %d\n", d1, d2, d3);
    printf("Sum: %d\n", sum);
    return 0;
}

20. Mini ATM Simulator

C

#include <stdio.h>

int main() {
    float balance = 500.0; // Initial bank balance
    int choice;
    float amount;

    printf("Current Balance: $%.2f\n", balance);
    printf("1. Deposit\n2. Withdraw\nChoose (1 or 2): ");
    scanf("%d", &choice);

    if (choice == 1) {
        printf("Enter deposit amount: ");
        scanf("%f", &amount);
        balance += amount;
        printf("Deposit successful! New Balance: $%.2f\n", balance);
    } else if (choice == 2) {
        printf("Enter withdrawal amount: ");
        scanf("%f", &amount);
        if (amount <= balance) {
            balance -= amount;
            printf("Withdrawal successful! Remaining Balance: $%.2f\n", balance);
        } else {
            printf("Insufficient funds! Transaction cancelled.\n");
        }
    } else {
        printf("Invalid option.\n");
    }

    return 0;
}