Question

I am facing a problem related to the scope of the variables used .

code:

   int row_no, upflag, downflag;
        for (int i = count; i > 0; i--)
        {
            asd = ds1.Tables[out_table].Rows[i][59].ToString();
            int com1 = string.Compare(asd, "Upstream");
            int com2 = string.Compare(asd, "Downstream");
            if (com1 == 0 || com2 == 0)
            {
                row_no = i;
                if (com1 == 0)
                    upflag = 1;
                else
                    downflag = 1; 
                break;
            }

        }
        if (upflag == 1)//
        {
            string val1 =  ds1.Tables[out_table].Rows[count][59].ToString();
            string val2 = ds1.Tables[out_table].Rows[(count - 1)][59].ToString();
        }

in this code, in the last if(upflag == 1) condition, my VS2010 shows a red line below the upflag and said
use of unassigned local variable ‘upflag’.

why is it so? It was perfectly ok in c++ , but here under multiple nested loops/condition, the value assigned to the variable inside the brackets, does not reflect back outside them, even when the variable is declared before the loop.

Please help

Answer 1

Consider what happens if count == 0. The body of the for loop will not be executed, and no value will be assigned to upflag. That’s why the compiler said “use of unassigned local variable” – it means it is possible that the variable was not assigned.

It was perfectly ok in c++

No, it wasn’t. The compiler might not have complained about it, but it was still undefined behaviour.