input: Write a function to convert a given Python program to a C# program. The function should take a string representation of the Python code as input and return a string representation of the equivalent C# code.
  assert convert_program_to_csharp("def power(x, y):\n    if y == 0:\n        return 1\n    else:\n        return x * power(x, y - 1)") == "public int Power(int x, int y)\n{\n    if (y == 0)\n    {\n        return 1;\n    }\n    else\n    {\n        return x * Power(x, y - 1);\n    }\n}"
  assert convert_program_to_csharp("def greet(name):\n    return f'Hello, {name}!'") == "public string Greet(string name)\n{\n    return $\"Hello, {name}!\";\n}"
  assert convert_program_to_csharp("") == ""
  assert convert_program_to_csharp("def simple_add(a, b):\n    return a + b") == "public int SimpleAdd(int a, int b)\n{\n    return a + b;\n}"
output: def convert_program_to_csharp(python_code):
      if not python_code:
          return ""
      
      lines = python_code.split('\n')
      csharp_code = []
      
      for line in lines:
          if line.startswith("def "):
              func_name, params = line[4:].split('(')
              params = params.split(')')[0]
              param_list = params.split(', ')
              csharp_params = []
              for param in param_list:
                  param_name, param_type = param.split(': ')
                  csharp_params.append(f"{param_type} {param_name}")
              csharp_params = ', '.join(csharp_params)
              return_type = "int" if "return" in python_code and "int" in python_code else "string"
              csharp_code.append(f"public {return_type} {func_name}({csharp_params})")
              csharp_code.append("{")
          elif line.startswith("    return "):
              return_value = line[11:]
              if return_value.startswith("f'"):
                  return_value = return_value.replace("f'", "$\"")
                  return_value = return_value.replace("'", "\"")
              csharp_code.append(f"    return {return_value};")
          elif line.startswith("    "):
              csharp_code.append(line.replace(":", "").replace("elif", "else if"))
          elif line.strip() == "":
              continue
          else:
              csharp_code.append(line)
      
      csharp_code.append("}")
      return '\n'.join(csharp_code)