Basic Math

 This is a pretty basic program that adds, subtracts, multiplies, or divides 2 numbers based on user input. I used a #define to create a shortcut for std::cout and the same can be done for std::endl if you wish to reduce how much typing you have to do.

Another interesting function I used is isDigit(x) which is part of the ctype.h library. It will return 0 if x is not a digit and something other than 0 if it is a digit. The reason I looped through the entire string is that if someone were to input 5gg and I only checked the first character it would come back as true and my atoi conversion would pick it up as only a 5, which could give unintended results. Since argv[] can be treated as a string I know it will end with a null byte and I just loop through to check every character till I reach the end.


#include<iostream>
#include<cstring>
#include<cstdlib>
#include<ctype.h>

#define COUT std::cout

int main(int argc, char *argv[])
{
    bool valid;
  
    if (argc == 4)
    {
        for(int i = 0; argv[1][i] != '\0'; i++) //checks if 1st argument is all digits
        {
            if(!isdigit(argv[1][i]))
                valid = false;  
        }
      
        for(int i = 0; argv[3][i] != '\0'; i++) //checks if 3rd argument is all digits
        {
            if(!isdigit(argv[3][i]))
                valid = false;  
        }

        if(valid)
        {
            double leftSide = atof(argv[1]);
            double rightSide = atof(argv[3]);

      
            //checks if 3rd argument is a valid operator then calculates - else prints error message
            if(strcmp(argv[2], "+") == 0)
                COUT << leftSide + rightSide << std::endl;
            else if(strcmp(argv[2], "-") == 0)
                COUT << leftSide - rightSide << std::endl;
            else if(strcmp(argv[2], "x") == 0)
                COUT << leftSide * rightSide << std::endl;
            else if(strcmp(argv[2], "/") == 0)
                COUT << leftSide / rightSide << std::endl;
            else
                COUT << "bm <number> <+-x/> <number>" << std::endl;
        }
        else
            COUT << "bm <number> <+-x/> <number>" << std::endl;
    }
    else
        COUT << "bm <number> <+-x/> <number>" << std::endl;

   
    return 0;
}