c# - Test Console.ReadLine(); input type -

i'm making console app in i'll ask user phone number int main_phone, if types string thats not convertible int such "caramel" want give him warning , ask number.

well thought recursive function do, i'm lacking logical aptitude one. came following code snippet:

static int? tryparse(string str) {     int tmp;     if (int.tryparse(str, out tmp)) {         return tmp;     }     return null; }//end of tryparse();  static int? verifyparse(string str, string lable) {     int? testedvar = tryparse(str);     if (testedvar == null)     {         console.writeline("este campo pode apenas conter dígitos de 0 à 9.");         console.write(lable);         verifyparse(console.readline(), lable);         return null;     }     else      {         return testedvar;     } }//end of verifyparse();  console.write("phone(main):");               int? main_phone = verifyparse(console.readline(),"telefone (principal):"); 

the problem if user inputs "string" main_phone comeback null, asks number between 0 , 9, if user passes convertible string , such "12", main_phone still null.

how can fix that?

edit 1:

what need function if string can converted int returns int, else gives me error , asks me input between 0 , 9. find hard because function have able return int or run self on again(to require , test valid input), can't because either returns int or doesn't return nothing.

edit 2:

here little update on problem:

static int tryparse(string lable)     {         string str = console.readline();          regex regex = new regex(@"\d+");          while (!regex.ismatch(str))         {             console.writeline("insira apenas dígitos de 0-9, por favor.");             console.write(lable);             str = console.readline();         }          return convert.toint32(str);     }//end of tryparse();      console.write("telefone (principal):");                  int main_phone = tryparse("telefone (principal):"); 

works well, except when input "1a". in case i'll error:

  system.formatexception: input string not in correct format.    @ system.number.stringtonumber(string str, numberstyles options, numberbuffer& number, numberformatinfo info, boolean parsedecimal)    @ system.number.parseint32(string s, numberstyles style, numberformatinfo info)    @ system.convert.toint32(string value)    @ app1.program.tryparse(string lable)    @ app1.program.main(string[] args)  

here's solution loops until match produced, using regex validation

regex regex = new regex(@"\d{3}-?\d{3}-?\d{4}"); string phonenumber = console.readline();  while (!regex.ismatch(phonenumber)) {     console.writeline("bad input");     phonenumber = console.readline(); }  return convert.toint32(phonenumber.replace("-","")); 

which match 5555555555 , 555-555-5555, , return int value.