Improvement to Adam's code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
int flag = 0;

double validate(char* x)
{
  int numOfDec = 0;
  int i = 0;

  if(x[i] == '-')
  {
    i++;
  }
/*   using lazy evaluation, this block of code can be shortened to 4 lines below
  while(x[i] != '\0')
  {
    if(!(isdigit(x[i])))
    {
      if(x[i] == '.')
      {
        numOfDec++;
        if((numOfDec) > 1)
        {
          flag = 1;
        }
      }
      else flag = 1;
    }
    i++;
  } */

while(x[i] != '\0'){

   (x[i] == '.') && (numOfDec+=1);

   ((numOfDec > 1) || (!(isdigit(x[i])))) && (flag = 1);

   i++;
}
  if(!flag)
    return atof(x);
  else
    return 0;
}

int main(int argc, char** argv)
{

  double newNum;
  // int numberOfDecimalPoingt = 0;       this variable is stated, but never used

  if(argc != 4)
  {
    flag = 1;
  }
  else
  {
    /*if(strlen(argv[2]) != 1)    this statement is taken out because it's not needed after modifying the validation underneath
    {
      flag = 1;
    }
    else */
      if(strcmp(argv[2],  "+")==0) newNum = validate(argv[1]) + validate(argv[3]);
      else if(strcmp(argv[2],  "-")==0) newNum = validate(argv[1]) - validate(argv[3]);
      else if(strcmp(argv[2],  "x")==0) newNum = validate(argv[1]) * validate(argv[3]);
      else if(strcmp(argv[2],  "/")==0) newNum = validate(argv[1]) / validate(argv[3]);
      else flag = 1;
  }

  if(flag)
  {
    printf("Format must be <number> <+-x/> <number>\n");
  }
  else
  {
    printf("%g\n", newNum);
  }

  return 0;
}

Simple Math problem OOP344

 /*The way I chose to do it is to use atof() after the parameters have passed each check, this way if there are any logic errors it would be easy to debug at each check point */

#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;
      //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;
}