Here is my implementation. This wil work for any number no matter how long.

#include

int SumOfNumbers(int x)

{

int sum = 0;

while (x)

{

sum += x % 10;

x /= 10;

}

return sum;

}

int main(int argc, char argv[])

{

std::string dob;

// her comes your stuff to ask for a number

int sumbrthdate = atoi(dob.c_str());

while ((sumbrthdate = SumOfNumbers(sum)) > 9);

return 0;

}

cout<<"Welcome to sum of birthdate Personlity test";

string dob;

cout<<"\nEnter your date of birth in this format DDMMYY"<
cin>>dob;

system("cls");

int sum=0;

string temp;

//cout<
if(dob.size()==6)

{

for(int i=0; i<6;i=i+2)

{

sum+=(static_cast(dob[i])-48)*10;

sum+=static_cast(dob[i+1]-48);

}

int sum1=0;

for(int i=0;i<3;i++)

{

sum1+=sum%10;

sum=sum/10;

}

int sumbrthdate =0;

for(int i=0;i<2;i++)

{

sumbrthdate +=sum1%10;

sum1=sum1/10;

}