C# Program to Convert Celsius to Fahrenheit

You can convert Celsius to Fahrenheit in C# using the formula fahrenheit = (celsius * 9 / 5) + 32. For example, double fahrenheit = (celsius * 9.0 / 5.0) + 32; converts a Celsius value to Fahrenheit.

Examples

Input0

Output32

Input25

Output77

Input-40

Output-40

How to Think About It

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9, then divide by 5, and finally add 32. This formula changes the scale from Celsius to Fahrenheit, which have different zero points and increments.

Algorithm

1

Get the temperature value in Celsius.

2

Multiply the Celsius value by 9.

3

Divide the result by 5.

4

Add 32 to the result.

5

Return or display the Fahrenheit temperature.

Code

csharp

using System;

class Program
{
    static void Main()
    {
        Console.Write("Enter temperature in Celsius: ");
        double celsius = Convert.ToDouble(Console.ReadLine());
        double fahrenheit = (celsius * 9.0 / 5.0) + 32;
        Console.WriteLine($"Temperature in Fahrenheit: {fahrenheit}");
    }
}

Output

Enter temperature in Celsius: 25
Temperature in Fahrenheit: 77

Dry Run

Let's trace converting 25 Celsius to Fahrenheit through the code

1

Input Celsius

User inputs 25

2

Multiply by 9

25 * 9 = 225

3

Divide by 5

225 / 5 = 45

4

Add 32

45 + 32 = 77

5

Output Fahrenheit

Print 77

Step	Operation	Value
1	Input Celsius	25
2	Multiply by 9	225
3	Divide by 5	45
4	Add 32	77
5	Output Fahrenheit	77

Why This Works

Step 1: Multiply Celsius by 9

Multiplying by 9 scales the Celsius temperature to match the Fahrenheit scale increments.

Step 2: Divide by 5

Dividing by 5 adjusts the scale ratio between Celsius and Fahrenheit degrees.

Step 3: Add 32

Adding 32 shifts the zero point from Celsius to Fahrenheit, aligning freezing points.

Alternative Approaches

Using a function

csharp

using System;

class Program
{
    static double CelsiusToFahrenheit(double celsius)
    {
        return (celsius * 9.0 / 5.0) + 32;
    }

    static void Main()
    {
        Console.Write("Enter Celsius: ");
        double c = Convert.ToDouble(Console.ReadLine());
        Console.WriteLine($"Fahrenheit: {CelsiusToFahrenheit(c)}");
    }
}

Separates conversion logic into a reusable function for cleaner code.

Using integer math (legacy)

csharp

using System;

class Program
{
    static void Main()
    {
        Console.Write("Enter Celsius: ");
        int celsius = Convert.ToInt32(Console.ReadLine());
        int fahrenheit = (celsius * 9 / 5) + 32;
        Console.WriteLine($"Fahrenheit: {fahrenheit}");
    }
}

Uses integer math which may lose precision; not recommended for decimal temperatures.

Complexity: O(1) time, O(1) space

Time Complexity

The calculation uses a fixed number of arithmetic operations, so it runs in constant time.

Space Complexity

Only a few variables are used, so space usage is constant.

Which Approach is Fastest?

All approaches run in constant time; using a function improves code reuse but does not affect speed.

Approach	Time	Space	Best For
Inline calculation	O(1)	O(1)	Simple quick conversion
Function method	O(1)	O(1)	Reusable and clean code
Integer math	O(1)	O(1)	Legacy code, less precise