Example: Body Mass Index (BMI) Calculator in C

// Body Mass Index (BMI) Calculator
#include <stdio.h>

int main() {
    float weight_kg; // Variable to store weight in kilograms
    float height_m;  // Variable to store height in meters
    float bmi;       // Variable to store the calculated BMI

    // Step 1: Prompt user for weight input
    printf("Welcome to the BMI Calculator!\n");
    printf("Please enter your weight in kilograms (e.g., 70.5): ");
    
    // Step 2: Read weight from user
    if (scanf("%f", &weight_kg) != 1) {
        printf("Invalid input for weight. Please enter a numerical value.\n");
        return 1; // Indicate an error
    }

    // Step 3: Prompt user for height input
    printf("Please enter your height in meters (e.g., 1.75): ");
    
    // Step 4: Read height from user
    if (scanf("%f", &height_m) != 1) {
        printf("Invalid input for height. Please enter a numerical value.\n");
        return 1; // Indicate an error
    }

    // Step 5: Check for invalid inputs (zero or negative height/weight)
    if (weight_kg <= 0 || height_m <= 0) {
        printf("Weight and height must be positive values. Please try again.\n");
        return 1; // Indicate an error
    }

    // Step 6: Calculate BMI using the formula: weight / (height * height)
    bmi = weight_kg / (height_m * height_m);

    // Step 7: Display the calculated BMI
    printf("\nYour calculated BMI is: %.2f\n", bmi); // .2f formats to two decimal places

    // Step 8: Provide BMI category interpretation for context
    printf("BMI Categories:\n");
    printf("  Underweight: < 18.5\n");
    printf("  Normal weight: 18.5 - 24.9\n");
    printf("  Overweight: 25 - 29.9\n");
    printf("  Obesity: >= 30\n");

    return 0; // Indicate successful execution
}