Question

I have problem with giving new char valure to array. I don’t know why I get sign “<” even when n is 12? My program should change expression int char* tab = "93+" to one value in this case 12.

    char* tab = "93+";
    int b = sizeof (tab);
    char* tmp = new char[b] ;
    tmp [b-1] = '\0';


if(isdigit(tab[i]) && isdigit(tab[i+1]) ){
               int n;             
               if(tab[i+2]=='+' || tab[i+2]=='-' || tab[i+2]=='*'){

                  switch(tab[i+2]){
                    case '+':   
                    n = (tab[i]-'0') + (tab[i+1]-'0');

                    break;

                    case '-':
                    n = (tab[i]-'0') - (tab[i+1]-'0');
                    break;

                    case '*':
                    n = (tab[i]-'0') * (tab[i+1]-'0');
                    break;
                  }
                  tmp[i] = n+'0'; // I should have 12 but I get <
               }

               else if (tab[i+2]!='+' || tab[i+2]!='-' || tab[i+2]!='*'){
                     goto LAB;
               }
}

Answer 1

The problem is in this line:

tmp[i] = n+'0'; // I should have 12 but I get <

n is 12, but 12 + ‘0’ != ’12’, since ’12’ isn’t a character. You’re putting into tmp[i] the char whose ascii value is 12 more than ‘0’, which is ‘<‘.
I believe declaring (and treating) tmp as an int would be better for your purposes.

Also note that sizeof (tab) is the same as sizeof (char *), and not sizeof ("93+"), so you’re likely to always get b==4 (in 32-bit machines).