Basic Math Program

#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
using namespace std;
#define NUM_OF_ARGUMENTS 4
void ErrorMessages(){
  cout<<"<number> <+-x/> <number><ENTER>"<<endl;
}
int main(int count, char* argv[]){
  double num1,num2;
  char operand;
  if( argv[2] != NULL)
    operand = argv[2][0];
  else{
    ErrorMessages();
    return 0;
  }
  if(count==NUM_OF_ARGUMENTS){
    if(sscanf(argv[1],"%lf",&num1)==1&&sscanf(argv[3],"%lf",&num2)==1){
      switch (operand) {
        case '+': cout << num1+num2<<endl; break;
        case '-': cout << num1-num2<<endl; break;
        case 'x': cout << num1*num2<<endl; break;
        case '/': cout << num1/num2<<endl; break;
        default: ErrorMessages(); break;
      }
    }
    else{
      ErrorMessages();
      return 0;
    }
  }
  else
    ErrorMessages();

  return 0;
}