C++ Convert char to intiger

Convert char to intiger with ATOI function.

#include <stdio.h>
#include <stdlib.h>

#define ArrSize 81
void main(){       // Conver char  to intiger with ATOI function
	char str[ArrSize] , arrNum[ArrSize] ;
	int  num , i=0 , ind=0 ;
	gets(str) ;
	while( (i<ArrSize) && (str[i]!='\0')  ) {
	  ind=0;
	  while ( (str[i]!=' ') && (str[i]>='0') && (str[i]<='9') ){
	   arrNum[ind] = str[i] ;
	   ind++ ; i++;
	  }
	 i++ ;
	 arrNum[ind]='\0' ;
         num=atoi(arrNum) ;
	 if (ind) printf("the number: %d \n",num);
	}
}