Python Program to Convert Temperature Between Celsius and Fahrenheit

You can convert temperature in Python using the formula F = (C * 9/5) + 32 for Celsius to Fahrenheit and C = (F - 32) * 5/9 for Fahrenheit to Celsius; for example, fahrenheit = (celsius * 9/5) + 32 converts Celsius to Fahrenheit.

Examples

Inputcelsius = 0

OutputFahrenheit: 32.0

Inputfahrenheit = 100

OutputCelsius: 37.78

Inputcelsius = -40

OutputFahrenheit: -40.0

How to Think About It

To convert temperature, first decide which scale you start with: Celsius or Fahrenheit. Use the correct formula to convert to the other scale by multiplying, dividing, and adding or subtracting constants. This is like changing units, for example, converting kilometers to miles by multiplying by a fixed number.

Algorithm

1

Get the temperature value and the scale it is in (Celsius or Fahrenheit).

2

If the scale is Celsius, apply the formula to convert to Fahrenheit.

3

If the scale is Fahrenheit, apply the formula to convert to Celsius.

4

Display the converted temperature with the correct scale.

Code

python

def celsius_to_fahrenheit(celsius):
    return (celsius * 9/5) + 32

def fahrenheit_to_celsius(fahrenheit):
    return (fahrenheit - 32) * 5/9

# Example usage
c = 25
f = celsius_to_fahrenheit(c)
print(f"{c}°C is {f:.2f}°F")

f2 = 77
c2 = fahrenheit_to_celsius(f2)
print(f"{f2}°F is {c2:.2f}°C")

Output

25°C is 77.00°F
77°F is 25.00°C

Dry Run

Let's trace converting 25°C to Fahrenheit and 77°F to Celsius through the code.

1

Convert 25°C to Fahrenheit

Calculate (25 * 9/5) + 32 = 45 + 32 = 77

2

Convert 77°F to Celsius

Calculate (77 - 32) * 5/9 = 45 * 5/9 = 25

Input	Operation	Result
25°C	(25 * 9/5) + 32	77°F
77°F	(77 - 32) * 5/9	25°C

Why This Works

Step 1: Formula for Celsius to Fahrenheit

Multiply the Celsius temperature by 9/5 and then add 32 to shift the scale to Fahrenheit.

Step 2: Formula for Fahrenheit to Celsius

Subtract 32 from the Fahrenheit temperature and multiply by 5/9 to convert back to Celsius.

Alternative Approaches

Using a single function with scale parameter

python

def convert_temperature(value, scale):
    if scale == 'C':
        return (value * 9/5) + 32
    elif scale == 'F':
        return (value - 32) * 5/9
    else:
        return None

print(convert_temperature(0, 'C'))  # 32.0
print(convert_temperature(32, 'F')) # 0.0

This method uses one function for both conversions, making the code shorter but requires checking the scale each time.

Using lambda functions

python

c_to_f = lambda c: (c * 9/5) + 32
f_to_c = lambda f: (f - 32) * 5/9

print(c_to_f(100))  # 212.0
print(f_to_c(212))  # 100.0

Lambda functions provide a concise way to write conversion formulas but may be less readable for beginners.

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

Time Complexity

The conversion uses simple arithmetic operations that take constant time regardless of input.

Space Complexity

Only a few variables are used to store input and output, so space usage is constant.

Which Approach is Fastest?

All approaches run in constant time; using separate functions or a single function with a parameter has no significant speed difference.

Approach	Time	Space	Best For
Separate functions	O(1)	O(1)	Clear and explicit conversions
Single function with scale	O(1)	O(1)	Compact code with scale check
Lambda functions	O(1)	O(1)	Concise one-liners, less readable