My while loop does not work - visual-c++

Question

i want to check the user input which cant larger than 2 and smaller than 1 as well as cant be char (because the input type is int) but my code seem not working.....anyone can help me out? I tried various way but seem i still get it
update: here is part the code , source is declared as int in previous part
Student stu;
List<Student> list;
char id[10];
string str;
int choice;
int source;
bool ask;
while(true){
switch(menu()) {
case 1:
{
system("cls");
if (ReadFile("student.txt", &list)) {
cout << "\nRead File Successfully!\n";
}
else
cout << "\nRead File Failed!\n";
system("pause");
break;
}
case 2:
{
system("cls");
if(list.empty()){
cout<<"\nThe list is empty!\n";
break;
}
cout<<"\nStudent id: ";
getline(cin,str);
while(!isdigit(str)){
cout<<"\nEnter [x] back to menu or re-enter the student id: ";
getline(cin,str);
if(str=="x"||str=="X"){
break;
}
}
strcpy_s(id,10,str.c_str());
if(DeleteRecord(&list, id)){
cout<<"\nStudent successfully deleted!\n";
}
else
cout<<"\nDelete student record failed!\n";
system("pause");
break;
}
case 3:
{
system("cls");
if(list.empty()){
cout<<"\nThe list is empty!\n";
break;
}
cout<<"\nStudent id: ";
getline(cin,str);
while(!isdigit(str)){
cout<<"\nEnter [x] back to menu or re-enter the student id: ";
getline(cin,str);
if(str=="x"||str=="X"){
break;
}
}
strcpy_s(id,10,str.c_str());
if(SearchStudent(&list, id, stu)){
cout<<"\nStudent record found!\n";
}
else
cout<<"\nStudent record not found!\n";
system("pause");
break;
}
case 4:
{
system("cls");
/*if(InsertResult("exam.txt",&list)) //Call InsertResult function
cout<<"*INSERT RESULT SUCCESSFULLY!"<<endl;
else
cout<<"*INSERT RESULT FAILED!"<<endl;
system("pause");
break;
}
case 5:
{
system("cls");
/*if(InsertSubject("subject.txt",&list)) //Call InsertSubject function
cout<<"*INSERT SUBJECT SUCCESSFULLY!"<<endl;
else
cout<<"*INSERT SUBJECT FAILED!"<<endl;*/
system("pause");
break;
}
case 6:
{
system("cls");
cout<<"\nWhere Do You Want To Display The Information?"<<endl;
cout<<"\n1.Screen."<<endl;
cout<<"\n2.File."<<endl;
cout<<endl;
cin>>source;
//check the input
while(!isdigit(source)||source<1||source>2)
{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}
cout<<"\nWhich Information Do You Want To Display?"<<endl;
cout<<"\n1.Student Information."<<endl;
cout<<"\n2.Student Information & Past Exam Result."<<endl;
cout<<"\n3.Student Information & Current Subject Taken."<<endl;
cout<<"\n4.Student Information & Past Exam Result & Current Subject Taken."<<endl;
cout<<endl;
cin>>choice;
//check the input
if(!isdigit(choice) || choice<1 || choice>2)
{
cout<<"\nPlease Enter A Valid Number Of Choice!"<<endl;
cin>>choice;
cout<<endl;
}
Display(&list,choice,source);
system("pause");
break;
}
case 7:
{
system("cls");
cout << "\nThank You For Using The Program!\n";
system("pause");
return 0;
}
}
}
cout << endl;
system("pause");
}

Answer 1

isdigit expects you to pass a character variable to it. The link I provided has an example:
/* isdigit example */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main ()
{
char str[]="1776ad";
int year;
if (isdigit(str[0]))
{
year = atoi (str);
printf ("The year that followed %d was %d.\n",year,year+1);
}
return 0;
}
You don't need to use isdigit because you are already using a int variable. Thus, this is the code you need:
case 6:
{
system("cls");
cout<<"\nWhere Do You Want To Display The Information?"<<endl;
cout<<"\n1.Screen."<<endl;
cout<<"\n2.File."<<endl;
cout<<endl;
cin>>source;
//check the input
while (source < 1 || source > 2)
{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}
}

Answer 2

cant larger than 2
source > 2
and smaller than 1
guessing you mean "can't be smaller than 1" source < 1
demo:
#include <iostream>
#include <ctype.h>
using namespace std;
int main(){
char source; // assuming source is char!!
cin>>source;
while(source < '1' || source > '2' || (!isdigit(source)) )
{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}
return 0;
}

Answer 3

Consider changing the code like this
while(!isdigit(source) || source < '1' || source > '2'))
{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}

Answer 4

Try this do-while loop Conditions,
do{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}while(source<1 || source>2 || !isdigit(source));
Edited
char digit; // holds only one char or one digit (0 1 2 3 ...9)
int source;
cin>>digit;
source=digit-'0'; // char to int
do{
cout<<"\nPlease Enter A Valid Number Of Source!"<<endl;
cin>>source;
cout<<endl;
}while(source<1 || source>2 || !isdigit(digit));//digit is character
In isdigit(arg) function,pass char argument its working fine.