Round argv[1] to the nearest integer

decToInt.cpp

/*
  This program rounds argv[1] to the nearest integer.
  
  It was tasked as a college programming assignment to one of my friends,
  and written by me (in this horrifying way so he couldn't steal it and
  turn it in)
*/

#include <iostream>

typedef std::runtime_error err;

int isd(char c) {
	return (c^0x30)<10;
}

int main_(int argc, char** argv) {
	++argv;
	int _ = 0, r = 0, d = **argv-'-'; 
	auto f = d?[](int a, int b) { return a+b; }:
	           [](int a, int b) { return a-b; };
	if(!d) ++*argv; 
	while(char c = *(*argv)++) 
	if(!isd(c)) 
	if(c == '.') 
	if(_++) goto e;
	else r = f(r,(**argv-'0')>=5);	
	else goto e;
	else if(!_) r = f(r*10, c-'0');
	std::cout << r << std::endl;
	return 0;
	e: throw err("Invalid input!");
}

int main(int argc, char** argv) {
	if(argc == 2) 
	try { return main_(argc, argv); }
	catch(err ex) { std::cout<<ex.what()<<std::endl; }
	std::cout<<"Usage: ./decToInt [decimal]"<<std::endl;
	return 1;
}