Modification to Zhen's Basic Math program

//Link to the original code see http://zenoop344.blogspot.ca/2013/09/include-include-include-int-mainint.html

#include <cstring>
#include <cstdlib>
#include <stdio.h>

int main(int argc, char** argv){
   if(!(argc==4)){      //check number of parameters
      printf("bm <number> <+-x/> <number><ENTER>\n");
      return 0;
   }
   //check if operator is valid 
   if((strcmp(argv[2], "+")!=0) && (strcmp(argv[2], "-")!=0) && (strcmp(argv[2], "/")!=0) && (strcmp(argv[2],         "x")!=0)){
      printf("bm <number> <+-x/> <number><ENTER>\n");
      return 0;
   }
   
   double left;
   double right;
   int i;
   int j;
   int dcounter;

   for(i=1; i<4; i+=2){
      dcounter=0;
//Added this code so as to accept parentheses      
//it just removes the parentheses before entering Zhen's checks,
// rather than output error message because of parentheses     
 if((argv[i][0] == 40) && (argv[i][strlen(argv[i])-1] == 41)){
      for(j=0; j<strlen(argv[i]); j++){            
          argv[i][j] = argv[i][j+1];     
      }    
      if(argv[i][(strlen(argv[i]))-1] == 41)
          argv[i][(strlen(argv[i]))-1] = '\0';
 }
      //check 1st element for invalid input, '-' is ok in the beginning for negative numbers
      if(((argv[i][0] < '0') || (argv[i][0] > '9')) && (argv[i][0] != '-')){
         printf("bm <number> <+-x/> <number><ENTER>\n");
         return 0;
      }
      (argv[i][0] == '.') && (dcounter+=1);         //check 1st element for decimal
      for(j=1; j<strlen(argv[i]); j++){                //check the rest of the array for invalid input
         (argv[i][j] == '.') && (dcounter+=1);
         if(dcounter>1){                                        //if more than 1 decimal
            printf("bm <number> <+-x/> <number><ENTER>\n");
            return 0;
         }
         if((argv[i][j] < '0' || argv[i][j] > '9') && argv[i][j] != '.'){ 
            printf("bm <number> <+-x/> <number><ENTER>\n");
            return 0;
         }
      }
   }
   left=atof(argv[1]);
   right=atof(argv[3]);
   (argv[2][0]=='+') && (printf("%g\n", left+right));
   (argv[2][0]=='-') && (printf("%g\n", left-right));
   (argv[2][0]=='x') && (printf("%g\n", left*right));
   (argv[2][0]=='/') && (printf("%g\n", left/right));
   return 0;
}