Fadi's Programming Blog

In Friday’s lecture Fardad (OOP344 Professor) assigned a second exercise for us to work on related to one of the topic’s of the lecture: command line arguments. The premise is simple: Write a program which receives two numbers and an operator from the command line in the format program_name number operator number and then output the result of the operation, also, error-checking must be included. An example run:

input ~> bm 2 x 2 output: 4 input ~> bm 4.6 + 5.7 output: 10.3 input ~> bm q w e output: invalid input! use format: <bm num op num>

    The first part of the problem: check the validity of the command line input. To do this I wrote a function called valid() which takes argc and argv as parameters and returns true if the input is found to be valid and false otherwise. If the input is detected as invalid the program will display an error message with a description of the proper use of the program and then exit allowing the user to try again with new input.

   The problem to solve is that the numbers provided in the command line are stored in the variable char* argv[] as strings. To perform any sort of mathematical operation on these numbers, they must first be converted to double values. To do this I used the function atof() from cstdlib which takes a null-terminated character array as an argument and returns a double value (if the string provided is convertible to a double, otherwise the function will return false).

   Finally, once the validity of the input is ensured and the strings have been converted to numbers, we’re ready to perform the arithmetic. Four if statements check for which operator was provided and the appropriate operation is performed and the answer displayed on screen.

My code:

//BasicMath.cpp //Fadi Tawfig //21/09/2013

#include <iostream> #include <cstdlib>

bool valid(int, char*[]);

int main(int argc, char* argv[]){ //First ensure that the command line variables provided are valid using  //valid() function. If not, exit the program with a message instructing the  //user on the proper use of the program. if(!valid(argc, argv)){ std::cout « “Invalid Input!” « std::endl « “Please enter an equation in the following format:” « std::endl; std::cout « “bm num operator(+, -, x, /) Example: bm 4 x 4” « std::endl; return 0; } //The atof() function included in cstdlib is used to convert a char* (string)  //to a double value double num1 = atof(argv[1]); double num2 = atof(argv[3]); //Find out which operator was used and print the result of the operation if(argv[2][0] == ‘+’) std::cout « std::endl « num1 + num2 « std::endl « std::endl; else if(argv[2][0] == ‘-‘) std::cout « std::endl « num1 - num2 « std::endl « std::endl; else if(argv[2][0] == ‘x’) std::cout « std::endl « num1 * num2 « std::endl « std::endl; else if(argv[2][0] == ‘/’) std::cout « std::endl « num1 / num2 « std::endl « std::endl; return 0; }

//Function valid() checks the validity of the input provided at the command line bool valid(int argc, char* argv[]){ //If the amount of command line arguments provided is not exactly four, //(program name, first number, operator and, second number) then the input //is invalid. if(argc != 4)  return false; //If the operator provided isn’t one of the four valid operators, then input //is invalid. else if(argv[2][0] != ‘+’ && argv[2][0] != ‘-’ && argv[2][0] != ‘x’ && argv[2][0] != ‘/’) return false; //If the 1st and 3rd arguments aren’t convertable to double values then the //input is invalid. else if(!atof(argv[1]) || !atof(argv[3])) return false; //If none of these conditions is true, the input valid() will return true. return true; }

I will be using this blog to write about my work in Seneca College's OOP344 course on C++ programming as well as any of my own programming projects I might be working on. Hope you enjoy reading.