Определение нужного типа

template<typename T>
BiggerType f(T t)
{
    BiggerType bt = t;
    return bt;
}

#include <iostream.h>
 
template <class T> 
T BiggerType (T t)
{
    T bt = t;
    return bt;
}
 
void main () {
    int iA=10 ; cout << "int  =" << BiggerType (iA)<<endl; 
  float fA=20.0 ; cout << "float  =" << BiggerType (fA)<<endl;  
 
}

#include <iostream.h>
 
template <class T,class T2> 
T2 BiggerType (T t,T2 a)
{
 
    T2 bt = (T2)t;
    return bt;
}
 
void main () {
    
  unsigned char iA='1' ; cout << "(unsigned long int)   =" << BiggerType (iA,(unsigned long int)1)<<endl; 
  float fA=20.5 ; cout << "int  =" << BiggerType (fA,(int)1)<<endl;  
 
}

#include <iostream>
#include <conio.h>
#include <typeinfo>
 
using namespace std;
 
template <typename T>
struct IntTraits
{
};
 
template <>
struct IntTraits<signed char>
{
    typedef signed long int BiggerType;
};
 
template <>
struct IntTraits<signed int>
{
    typedef signed long int BiggerType;
};
 
// ...аналогично для signed short int и signed long int
 
template <>
struct IntTraits<unsigned char>
{
    typedef unsigned long int BiggerType;
};
 
template <>
struct IntTraits<unsigned int>
{
    typedef unsigned long int BiggerType;
};
 
// ...аналогично для unsigned short int и unsigned long int
 
template <typename T>
typename IntTraits<T>::BiggerType f(T t)
{
    return t;
}
 
int main()
{
    signed char c = 1;
    unsigned short us = -1;
    cout << typeid(c).name() << " => " << typeid(f(c)).name() << endl;
    cout << typeid(us).name() << " => " << typeid(f(us)).name() << endl;
    getch();
    return 0;
}