C Programming Day 7: Week 1 Review & Mini Project - Building a Calculator

(Learn C Programming for Beginners — Day 7)

Congratulations! 🎉 You’ve made it to Day 7 of your 30-Day C Programming Adventure!

You’ve survived the first week. You’ve gone from "What is a compiler?" to writing code that can talk, listen, and do math. That is a huge achievement.

Today is a Milestone Day. We aren't learning new syntax today. Instead, we are going to:
1. Review everything we've learned in Week 1.
2. Build a Mini Project — A fully functional Simple Calculator.
3. Celebrate your progress!

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🔄 Week 1 Recap: The Foundation

Let's quickly look back at the tools you've added to your belt:

• Day 1 & 2: You set up your environment (VS Code + GCC) and wrote the legendary Hello, World!.
• Day 3: You learned about Variables (int, float, char) — the boxes that hold your data.
• Day 4: You mastered Input/Output (printf, scanf) — making your programs interactive.
• Day 5: You unlocked Operators (+, -, %, ==, &&) — the math and logic engines.
• Day 6: You learned Code Style — writing clean, readable code with comments and proper indentation.

You have all the ingredients. Now, let's cook.

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🛠️ Mini Project: The Simple Calculator

We are going to build a program that asks the user for two numbers and then performs addition, subtraction, multiplication, and division on them.

The Plan:

1. Greet the user.
2. Ask for two numbers.
3. Perform calculations (Sum, Difference, Product, Quotient, Remainder).
4. Display the results neatly.

Step 1: Create the File

Create a new file named day7_calculator.c.

Step 2: Write the Code

Try to write it yourself first! If you get stuck, here is the solution:

/*
    Project: Simple Calculator (Week 1 Milestone)
    Author: [Your Name]
    Date: [Today's Date]
    Description: A program that takes two integers and performs basic arithmetic.
*/

#include <stdio.h>

int main() {
    // 1. Declare Variables
    int num1, num2;
    int sum, diff, prod, rem;
    float quot; // Quotient needs to be a float for decimal precision

    // 2. Input
    printf("====================================\n");
    printf("\tSIMPLE CALCULATOR v1.0\n");
    printf("====================================\n\n");

    printf("Enter the first number: ");
    scanf("%d", &num1);

    printf("Enter the second number: ");
    scanf("%d", &num2);

    // 3. Calculations
    sum = num1 + num2;
    diff = num1 - num2;
    prod = num1 * num2;

    // Typecasting: We convert one integer to float to get a decimal result
    quot = (float)num1 / num2; 

    rem = num1 % num2;

    // 4. Output
    printf("\n--- Results ---\n");
    printf("Addition:\t%d + %d = %d\n", num1, num2, sum);
    printf("Subtraction:\t%d - %d = %d\n", num1, num2, diff);
    printf("Multiplication:\t%d * %d = %d\n", num1, num2, prod);
    printf("Division:\t%d / %d = %.2f\n", num1, num2, quot);
    printf("Modulus:\t%d %% %d = %d\n", num1, num2, rem); // Note: %% prints a single %

    printf("\nThank you for using the calculator!\n");

    return 0;
}

Step 3: Compile and Run

• gcc day7_calculator.c -o calculator
• ./calculator

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🧠 Key Concepts in Action

1. Typecasting: Did you notice (float)num1?

   • If we just did num1 / num2 (e.g., 5 / 2), C would do integer division and give us 2.
   • By putting (float) in front, we force C to treat num1 as a decimal number (5.0), so the result becomes 2.5. This is a pro tip!

2. Escape Sequences: We used \t to align the text and \n for spacing.

3. Printing %: To print the actual percent symbol in printf, you have to type it twice: %%.

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🚀 Challenge: The "Tip Calculator"

Want to push yourself further? Modify your calculator to be a Tip Calculator.
1. Ask for the Bill Amount (float).
2. Ask for the Tip Percentage (int).
3. Calculate the Tip Amount (bill * percentage / 100).
4. Calculate the Total Bill (bill + tip).
5. Print the receipt.

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🔮 What's Next? Week 2 Preview

You've mastered the basics. Next week, we give your programs a brain.

• Week 2 is all about Control Flow.
• You'll learn how to make your code make decisions (if/else).
• You'll learn how to repeat tasks (loops) without writing the same code 100 times.

Get some rest, celebrate your Week 1 victory, and I'll see you on Day 8!

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