calculating reveres and summation

[Rousan]

can some one tell where is the error?


#include <iostream>
#include <string>
using namespace std;
void ReverseInputDigit (int I);
void SumDigit (int S);
int main ()
{
int I=0,S=0;
char f;
cout<<"please insert"<<endl;
cout<<"I for calculating Reverse Input Digit or S for calculating the summation of the digits"<<endl;
cin>>f;
if(f == 'I')
{
ReverseInputDigit (I);
}
if(f == 'S')
{
SumDigit (S);
}
return 0;

}
void ReverseInputDigit (int I)
{
cout<<"Please insert a number to reverse: ";
cin>>I;
cout<<"The reverse of "<<I<<" is " <<I % 10<<(I/10) % 10<<(I/100) % 10<<(I/1000) % 10<<(I/10000)% 10<<endl;//just 5 places!//
}
void SumDigit (int S)
{
cout<<"Please insert a any number "<<endl;
cin>>S;
cout<<"The summation of "<<S<< " is "<< (S % 10)+((S/10) % 10)+((S/100) % 10)+((S/1000) % 10)+((S/10000)% 10)<<endl;//just 5 places!//
}

[KRAkatau]

what seems to be an error? it works ok for 5-digit numbers.