input: Write a function to convert a given temperature from Celsius to Fahrenheit. The function should take the temperature in Celsius as input and return the equivalent temperature in Fahrenheit.
  assert celsius_to_fahrenheit(0)==32.0
  assert celsius_to_fahrenheit(100)==212.0
  assert celsius_to_fahrenheit(-40)==-40.0
  assert celsius_to_fahrenheit(37)==98.6
  assert celsius_to_fahrenheit(25)==77.0
output: def celsius_to_fahrenheit(celsius):
      return celsius * 9/5 + 32