Exercise C++ input/output

• Reading (writing) numbers into (out of) your C++ program.

Tasks:

1. Command-line

   Read a set of numbers from the command-line argument in the form (we follow the Unix option convension),

   ./main -n 1 -n 2 -n 3 -n 4 -n 5 > Out.txt 

   and print these numbers together with their sines and cosines (in a table form) to the standard output. Something like

   int main (int argc, char* argv[]) {
   	std::vector<double> numbers;
   	for(int i=0;i<argc;++i){
   		std::string arg=argv[i];
   		if(arg=="-n" && i+1<argc)
   			numbers.push_back(std::stod(argv[i+1]));
   	}
   for(auto n: numbers)
   	std::cout << n <<" "<< std::sin(n) <<" "<< std::cos(n) <<std::endl;
   exit(EXIT_SUCCESS);
   }
   

   The program can get the numbers from the command-line directly,

   ./main -n 1 -n 2 -n 3 -n 4 -n 5 > out.txt
   

   or, alternatively, if the line of numbers is too long, one can write the numbers into a file and then "cat" the file into the command line,

   echo "-n 1 -n 2 -n 3 -n 4 -n 5" > inputfile
   ./main $(cat inputfile) > out.txt
   

   The length of the command line is limited though, so the size of the file should not exceed your command line limit (probably about 2 megabytes).

2. Standard input stream

   Read a sequence of numbers from the standard input and print these numbers together with their sines and cosines (in a table form) to the standard output. Something like

   double x;
   while( std::cin >> x ){
   	std::cout << x <<" "<< std::sin(x) <<" "<< std::cos(x) << std::endl;
   	}
   

   The program can be run as

   echo 1 2 3 4 5 | ./main > out.txt 

   or

   echo 1 2 3 4 5 > input.txt
   ./main < input.txt > out.txt
   

   or

   echo 1 2 3 4 5 > input.txt
   cat input.txt | ./main > out.txt
   

3. File streams

   Read a set of numbers separated by whitespaces from "inputfile" and write them together with their sines and cosines (in a table form) to "outputfile". The program must read the names of the "inputfile" and "outputfile" from the command-line,

   ./main --input my_input_file.txt --output my_output_file.txt
   

   Something like

   int main (int argc, char *argv[]) {
   	std::string infile="", outfile="";
   	for(int i=0;i<argc;i++){
   		std::string arg=argv[i];
   		if(arg=="--input" && i+1 < argc) infile=argv[i+1];
   		if(arg=="--output" && i+1 < argc) outfile=argv[i+1];
   	}
   std::ifstream myinput(infile);
   std::ofstream myoutput(outfile);
   double x;
   if( myinput.is_open() && myoutput.is_open() ){
   	while( myinput >> x ){
   		myoutput << x <<" "<<std::sin(x)<<" "<<std::cos(x)<<std::endl;
   		}
   	}
   else{
   	std::cerr << "Error opening files: " << infile << outfile << std::endl;
   	return EXIT_FAILURE;
       }
   myinput.close();
   myoutput.close();
   exit(EXIT_SUCCESS);
   }