Using command line arguments

[Jason]

I am suppose to create a small program that uses command line arguments. Its suppose to be executable as pgm1 -c, if 'c' is 'o' then its suppose to output the sum of odd integers 1-100, if 'c' is 'e' then its suppose to output the sum of even integers 1-100. If c is any other char, it should print an error message. Here is my code but when i try to use a command line argument when i run it nothing happens and i just get another prompt. Could somebody pls point me in the write direction. Thanks a lot.

#include<iostream>
using namespace std;

int sumOdd();
int sumEven();

int main(int argc, char *argv[])
{
switch(argc)
{
case1: break;
case2: if(strcmp(argv[1], "-o") == 0) cout<<"The sum of odd numbers from 1-100 is "<<sumOdd()<<endl;
else if(strcmp(argv[1], "-e") == 0) cout<<"The sum of even numbers from 1-100 is "<<sumEven()<<endl;
else cout<<"Invalid Argument"<<endl;

default:;
}

return 0;
}

int sumOdd()
{
int total = 0;

for(int i = 1; i < 100; i + 2)
total = total + i;

return total;
}

int sumEven()
{
int total = 0;

for(int i = 0; i < 100; i + 2)
total = total + i;

return total;
}

[jgbauman]

1. This loops wont work:
   

   for(int i = 0; i < 100; i + 2)

   
   You need i += 2 to modify i.
2. You stumpled across some of the more obscure aspects of the C/C++ syntax:
   name: defines a label which can be used as target for goto. Yes there is a goto in C++, really ;-)
   The switch case uses this syntax for the default: label, too.
   The cases use it in a modified form case <integer>:.
   But if you forget the whitespace like you did, they become ordinary goto labels without sepcial meaning to the switch statement.
   So
   

   Code: Select all

     switch(argc) {
  case1:
    break;
  case2:
    if(strcmp(argv[1], "-o") == 0)
      cout << "The sum of odd numbers from 1-100 is " << sumOdd() << endl;
    else if(strcmp(argv[1], "-e") == 0)
      cout << "The sum of even numbers from 1-100 is " << sumEven() << endl;
    else
      cout << "Invalid Argument" << endl;
  default:;
  }


   
   is equivalent to (since case1 and case2 are unused goto labels)
   

   Code: Select all

     switch(argc) {
    break;
    if(strcmp(argv[1], "-o") == 0)
      cout << "The sum of odd numbers from 1-100 is " << sumOdd() << endl;
    else if(strcmp(argv[1], "-e") == 0)
      cout << "The sum of even numbers from 1-100 is " << sumEven() << endl;
    else
      cout << "Invalid Argument" << endl;
  default:;
  }


   
   is equivalent to (since it breaks out of the switch for every input)
   

   Code: Select all

     switch(argc) {
    break;
  }


   
   is equivalent to
   

   Code: Select all

     /* do nothing but irritate programmers */


   
   
   

[Tracer]

/* do nothing but irritate programmers */

, good times...

[Jason]

Ok I see it now, stupid me, I shold of saw that. Thanks a lot for the help.