spliting string input and find if characters are valid - c++

Question

It is possible to do next:
Let say I have a string "input" (that will be a input), I will cut this input in 2 parts, next, I will find if I entered first part only letters, and second part only digits? the code work only for letters but not for digits(remove comments, to see that all entered will be valid)
#include <iostream>
#include <string>
#include <iomanip>
#include <cctype>
using namespace std;
int main ()
{
while (true)
{
bool flag = false; // to check for numeric entry
string input; // not req to initialize
string input1;
cout << "Enter the string like ABC 123: ";
getline (cin, input);
if (input == "")
{
flag = true;
}
if (string::size_type pos = input.find (' '))//spliting the input in 2 if it will find a space
{
if (input.npos != pos)
{
input1 = input.substr (pos + 1);
input = input.substr (0, pos);
}
}
for (int i = 0; i < input.size (); i++)
{
// for (int n = 0; i < input1.size (); i++)
// {
int uppercaseCHar = toupper (input[i]);//checking if input(first part) contains only letters
if (!std::isalpha (uppercaseCHar))
{
// if(isdigit(input1[n]) == 0)//checing if input1(second part) contains only digits
// {
flag = true;
break;
// }
}
// }
}
if (input.compare ("1") == 0) break;//This will end program
{
flag = false;
}
if (flag)
{
cout << "Invalid!\n";
cout << endl;
} else
{
cout << "The string is valid! \n";
cout << endl;
}
}
}
Enter the string like ABC 123: QWE 123
The string is valid!
Enter the string like ABC 123: QW1 123
Invalid!

Answer 1

I don't have rights to comment yet, but if your first and second part of string don't have to be of same length, you can use the for loop two times for each sub string and then compare the values by one character at a time.
Also after checking for termination condition by
if (input.compare ("1") == 0) break;
you are adding a statement
{
flag = false;
}
this will set the result to false even if you have compared in your loop and found it TRUE,so take a look at following code below, i have commented that block of code out.
#include <iostream>
#include <string>
#include <iomanip>
#include <cctype>
using namespace std;
int main ()
{
while (true)
{
bool flag = false; // to check for numeric entry
string input; // not req to initialize
string input1;
cout << "Enter the string like ABC 123: ";
getline (cin, input);
if (input == "")
{
flag = true;
}
if (string::size_type pos = input.find (' '))//spliting the input in 2 if it will find a space
{
if (input.npos != pos)
{
input1 = input.substr (pos + 1);
input = input.substr (0, pos);
}
}
//cout<<"\n"<<input1;
//cout<<"\n"<<input;
//First check the letter part (first part) if it contains digits
for(int i=0;i<input.size();i++){
if(!std::isalpha(input[i])){
flag=true;
break;
}
}
//second check if the numeric part (second part) only contains digits
for(int i=0;i<input1.size();i++){
if(!std::isdigit(input1[i])){
flag=true;
break;
}
}
/*
for (int i = 0; i < input.size (); i++)
{
for (int n = 0; i < input1.size (); i++)
{
int uppercaseCHar = toupper (input[i]);//checking if input(first part) contains only letters
if (!std::isalpha (uppercaseCHar))
{
if(isdigit(input1[n]) == 0)//checing if input1(second part) contains only digits
{
flag = true;
break;
}
}
}
}
*/
if (input.compare ("1") == 0) break;//This will end program
//after checking for break, if you add flag=false, it will automatically ignore whatever flag you set, and you will always find FLAG=FALSE when compairing in upcoming lines
//{
// flag = false;
//}
if (flag)
{
cout << "Invalid!\n";
cout << endl;
} else
{
cout << "The string is valid! \n";
cout << endl;
}
}
}