HOW to Change the value of a global variable in local scope without overriding
int val; while (sqlReader.Read()) { if (textBox_reg_login.Text == sqlReader["login"].ToString()) { label_reg_login_message.Text = "Логин с таким значением уже существует"; val = 1; //Глобальная переменная переопределяется break; } } if (val == 1) //И здесь уже ошибка: переменной val не присвоено значение { } 
Where the error comes from is clear: after all, nothing guarantees that within the while value of the variable val will be assigned. And reading an uninitialized variable in the language is not allowed.
Initialize val with some value before the loop.
And by the way, you have a val , apparently, a local variable. Class fields (both simple and static) are initialized by default to the default value of the corresponding type.
Source: https://ru.stackoverflow.com/questions/819385/
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