A C Sharp BMI and BMR Calculator program with code explanation

Below is a C# BMI and BMR Calculator program.

The program calculates the Body Mass Index (BMI) and Basal Metabolic Rate (BMR) based on user input for weight, height, age, and gender.

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Full Code

using System;

class BMICalculator
{
    static void Main(string[] args)
    {
        Console.WriteLine("Welcome to the BMI and BMR Calculator!");

        // Collect user inputs
        Console.Write("Enter your weight in kilograms: ");
        double weight = GetValidInput();

        Console.Write("Enter your height in meters: ");
        double height = GetValidInput();

        Console.Write("Enter your age in years: ");
        int age = (int)GetValidInput();

        Console.Write("Enter your gender (Male/Female): ");
        string gender = Console.ReadLine().Trim().ToLower();

        // Calculate BMI
        double bmi = CalculateBMI(weight, height);
        Console.WriteLine($"\nYour BMI is: {bmi:F2}");
        Console.WriteLine($"BMI Category: {BMICategory(bmi)}");

        // Calculate BMR
        double bmr = CalculateBMR(weight, height, age, gender);
        if (bmr > 0)
        {
            Console.WriteLine($"Your BMR is: {bmr:F2} calories/day");
        }
        else
        {
            Console.WriteLine("Invalid gender entered. Unable to calculate BMR.");
        }
    }

    static double GetValidInput()
    {
        double value;
        while (true)
        {
            if (double.TryParse(Console.ReadLine(), out value) && value > 0)
            {
                return value;
            }
            else
            {
                Console.Write("Invalid input. Please enter a positive numeric value: ");
            }
        }
    }

    static double CalculateBMI(double weight, double height)
    {
        return weight / (height * height);
    }

    static string BMICategory(double bmi)
    {
        if (bmi < 18.5) return "Underweight";
        if (bmi >= 18.5 && bmi < 24.9) return "Normal weight";
        if (bmi >= 25 && bmi < 29.9) return "Overweight";
        return "Obesity";
    }

    static double CalculateBMR(double weight, double height, int age, string gender)
    {
        if (gender == "male")
        {
            // Harris-Benedict formula for men
            return 10 * weight + 6.25 * (height * 100) - 5 * age + 5;
        }
        else if (gender == "female")
        {
            // Harris-Benedict formula for women
            return 10 * weight + 6.25 * (height * 100) - 5 * age - 161;
        }
        else
        {
            // Invalid gender
            return -1;
        }
    }
}

Explanation

1. Introduction

• The program starts by greeting the user and providing a simple interface for inputting data such as weight, height, age, and gender.

2. User Input Validation

• The GetValidInput method ensures all numeric inputs (weight, height, and age) are positive numbers.
• If the user enters invalid data, the program prompts them to try again until a valid input is provided.

static double GetValidInput()
{
    double value;
    while (true)
    {
        if (double.TryParse(Console.ReadLine(), out value) && value > 0)
        {
            return value;
        }
        else
        {
            Console.Write("Invalid input. Please enter a positive numeric value: ");
        }
    }
}

3. BMI Calculation

• The Body Mass Index (BMI) is calculated using the formula: BMI=weightheight2BMI = \frac{\text{weight}}{\text{height}^2}
• The result is formatted to two decimal places and categorized based on standard BMI categories.

static double CalculateBMI(double weight, double height)
{
    return weight / (height * height);
}

static string BMICategory(double bmi)
{
    if (bmi < 18.5) return "Underweight";
    if (bmi >= 18.5 && bmi < 24.9) return "Normal weight";
    if (bmi >= 25 && bmi < 29.9) return "Overweight";
    return "Obesity";
}

Example:

• Weight: 70 kg
• Height: 1.75 m
• BMI = 701.752=22.86\frac{70}{1.75^2} = 22.86 (Normal weight)

4. BMR Calculation

• The Basal Metabolic Rate (BMR) is calculated using the Harris-Benedict formula:
  • For Males: BMR=10⋅weight+6.25⋅height (cm)−5⋅age+5BMR = 10 \cdot \text{weight} + 6.25 \cdot \text{height (cm)} – 5 \cdot \text{age} + 5
  • For Females: BMR=10⋅weight+6.25⋅height (cm)−5⋅age−161BMR = 10 \cdot \text{weight} + 6.25 \cdot \text{height (cm)} – 5 \cdot \text{age} – 161
• The program validates gender input and calculates BMR accordingly. If the gender is invalid, it returns -1.

static double CalculateBMR(double weight, double height, int age, string gender)
{
    if (gender == "male")
    {
        return 10 * weight + 6.25 * (height * 100) - 5 * age + 5;
    }
    else if (gender == "female")
    {
        return 10 * weight + 6.25 * (height * 100) - 5 * age - 161;
    }
    else
    {
        return -1;
    }
}

Example:

• Weight: 70 kg
• Height: 1.75 m (converted to 175 cm)
• Age: 25 years
• Gender: Male
• BMR = 10⋅70+6.25⋅175−5⋅25+5=1653.75 calories/day10 \cdot 70 + 6.25 \cdot 175 – 5 \cdot 25 + 5 = 1653.75 \, \text{calories/day}

5. Output

• The program displays:
  • BMI with its category (e.g., Normal weight, Overweight).
  • BMR with a message indicating daily calorie requirements.

Console.WriteLine($"\nYour BMI is: {bmi:F2}");
Console.WriteLine($"BMI Category: {BMICategory(bmi)}");
Console.WriteLine($"Your BMR is: {bmr:F2} calories/day");

Sample Run

Example Run:

Welcome to the BMI and BMR Calculator!
Enter your weight in kilograms: 70
Enter your height in meters: 1.75
Enter your age in years: 25
Enter your gender (Male/Female): Male

Your BMI is: 22.86
BMI Category: Normal weight
Your BMR is: 1653.75 calories/day

Invalid Input Example:

Enter your weight in kilograms: -50
Invalid input. Please enter a positive numeric value: 70

Gender Validation Example:

Enter your gender (Male/Female): Unknown
Invalid gender entered. Unable to calculate BMR.

Features

1. Input Validation:
   • Ensures weight, height, and age are positive numbers.
   • Handles invalid or unexpected gender inputs.
2. BMI Calculation:
   • Calculates BMI using a standard formula and categorizes it based on health guidelines.
3. BMR Calculation:
   • Calculates daily calorie requirements based on the Harris-Benedict formula, considering gender, weight, height, and age.
4. Reusable Methods:
   • Modular design with separate methods for BMI and BMR calculations, input validation, and BMI categorization.

Ideas for Enhancement

1. Activity Factor:
   • Include activity levels (e.g., sedentary, active) to estimate total daily energy expenditure (TDEE).

   Example:

   Console.Write("Enter your activity level (Sedentary, Active, Very Active): ");
   

2. Unit Conversion:
   • Allow users to input height in feet/inches or weight in pounds, then convert to metric.
3. Save Results:
   • Save BMI and BMR results to a file for future reference.
4. Graphical User Interface:
   • Use Windows Forms or WPF to create a user-friendly interface.

This C# BMI and BMR Calculator provides a simple yet effective way to calculate key health metrics