Example: Temperature Converter & Water State Identifier in C

// Temperature Converter & Water State Identifier
#include <stdio.h>

// Function to convert Celsius to Fahrenheit
float celsiusToFahrenheit(float celsius) {
    return (celsius * 9 / 5) + 32;
}

// Function to convert Fahrenheit to Celsius
float fahrenheitToCelsius(float fahrenheit) {
    return (fahrenheit - 32) * 5 / 9;
}

// Function to convert Celsius to Kelvin
float celsiusToKelvin(float celsius) {
    return celsius + 273.15;
}

// Function to convert Kelvin to Celsius
float kelvinToCelsius(float kelvin) {
    return kelvin - 273.15;
}

// Function to determine the state of water
void determineWaterState(float tempCelsius) {
    if (tempCelsius <= 0) {
        printf("At %.2f Celsius, water is in a Solid (Ice) state.\n", tempCelsius);
    } else if (tempCelsius < 100) {
        printf("At %.2f Celsius, water is in a Liquid state.\n", tempCelsius);
    } else {
        printf("At %.2f Celsius, water is in a Gaseous (Steam) state.\n", tempCelsius);
    }
}

int main() {
    float temperature;
    char scale_char; // 'C' for Celsius, 'F' for Fahrenheit, 'K' for Kelvin
    int choice;

    // Step 1: Get user input for temperature and initial scale
    printf("Enter temperature value: ");
    scanf("%f", &temperature);
    printf("Enter original scale (C for Celsius, F for Fahrenheit, K for Kelvin): ");
    scanf(" %c", &scale_char); // Note the space before %c to consume newline

    float tempCelsius; // Store temperature in Celsius for consistent internal calculations

    // Step 2: Convert input to Celsius for standardized processing
    switch (scale_char) {
        case 'C':
        case 'c':
            tempCelsius = temperature;
            break;
        case 'F':
        case 'f':
            tempCelsius = fahrenheitToCelsius(temperature);
            break;
        case 'K':
        case 'k':
            tempCelsius = kelvinToCelsius(temperature);
            break;
        default:
            printf("Invalid scale entered. Exiting.\n");
            return 1; // Indicate an error
    }

    // Step 3: Provide options to the user
    printf("\nChoose an option:\n");
    printf("1. Convert to all scales\n");
    printf("2. Determine state of water\n");
    printf("3. Both (Convert and Determine state)\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);

    // Step 4: Execute chosen option
    if (choice == 1 || choice == 3) {
        printf("\n--- Conversions ---\n");
        printf("Original: %.2f %c\n", temperature, scale_char);
        printf("Celsius: %.2f C\n", tempCelsius);
        printf("Fahrenheit: %.2f F\n", celsiusToFahrenheit(tempCelsius));
        printf("Kelvin: %.2f K\n", celsiusToKelvin(tempCelsius));
    }

    if (choice == 2 || choice == 3) {
        printf("\n--- Water State ---\n");
        determineWaterState(tempCelsius);
    }

    // Note: For other substances, you would define their specific freezing/boiling points
    // and create a similar function to 'determineWaterState'.
    // E.g., for Ethanol: Freezing point ~ -114.1°C, Boiling point ~ 78.37°C

    return 0;
}