#include "std_lib_facilities.h"

class Below_zero {};
constexpr double ABSOLUTE_ZERO = 0;
constexpr double ABS_ZERO_C = -273.15;

double ctok(double c)
{
	try{
          	double k = c - ABS_ZERO_C;
          	if (k < ABSOLUTE_ZERO)
          		throw Below_zero{};
          	return k;
        }

}

double ktoc(double k)
{
	try{
		double c = k+ABS_ZERO_C;
		if (c < ABS_ZERO_C)
			throw Below_zero{};

		return c;
	}

}

int main()
{

while(cin){

	cout << "Please enter a number followed by C or K to denote Kelvin or Celsius, then press 'enter'\n";

        	double b = 0;
        	string u = "";
          	cin >> b >> u;
          	if (u == "c" || u == "C"){
          		double r = ctok(b);
          		u = " K";
          		cout << r << u << '\n' ;
          		//return 0;
          	}
          	else if (u == "k" || u == "K"){
          		double r = ktoc(b);
			try{
          			u = " C";
          			cout << r << u << '\n';
          			//return 0;
          		}
          	}
          	else{
          		error("invalid unit");
          		return 2;
		}

	catch (Below_zero){
		cerr << "lower than absolute zero.\n";
	return 1;
	}
}



}




merockstar@merockstar-HP-Pavilion-dv6-Notebook-PC:~/1CPPAttempt$ g++ -std=c++11 -Wall -Wextra -pedantic -O3 ch5ex2.cpp
In file included from ch5ex2.cpp:1:0:
std_lib_facilities.h: In member function ‘char& String::operator[](unsigned int)’:
std_lib_facilities.h:107:9: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
   if (i<0||size()<=i) throw Range_error(i);
         ^
std_lib_facilities.h: In member function ‘const char& String::operator[](unsigned int) const’:
std_lib_facilities.h:113:9: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
   if (i<0||size()<=i) throw Range_error(i);
         ^
ch5ex2.cpp: In function ‘double ctok(double)’:
ch5ex2.cpp:16:1: error: expected ‘catch’ before ‘}’ token
 }
 ^
ch5ex2.cpp:16:1: error: expected ‘(’ before ‘}’ token
ch5ex2.cpp:16:1: error: expected type-specifier before ‘}’ token
ch5ex2.cpp:16:1: error: expected ‘)’ before ‘}’ token
ch5ex2.cpp:16:1: error: expected ‘{’ before ‘}’ token
ch5ex2.cpp: In function ‘double ktoc(double)’:
ch5ex2.cpp:28:1: error: expected ‘catch’ before ‘}’ token
 }
 ^
ch5ex2.cpp:28:1: error: expected ‘(’ before ‘}’ token
ch5ex2.cpp:28:1: error: expected type-specifier before ‘}’ token
ch5ex2.cpp:28:1: error: expected ‘)’ before ‘}’ token
ch5ex2.cpp:28:1: error: expected ‘{’ before ‘}’ token
ch5ex2.cpp: In function ‘int main()’:
ch5ex2.cpp:53:12: error: expected ‘catch’ before ‘}’ token
            }
            ^
ch5ex2.cpp:53:12: error: expected ‘(’ before ‘}’ token
ch5ex2.cpp:53:12: error: expected type-specifier before ‘}’ token
ch5ex2.cpp:53:12: error: expected ‘)’ before ‘}’ token
ch5ex2.cpp:53:12: error: expected ‘{’ before ‘}’ token
ch5ex2.cpp:59:2: error: expected primary-expression before ‘catch’
  catch (Below_zero){
  ^
ch5ex2.cpp:59:2: error: expected ‘;’ before ‘catch’
merockstar@merockstar-HP-Pavilion-dv6-Notebook-PC:~/1CPPAttempt$