~cpp
#include <stdio.h>
#include <stdarg.h>

int sum(int n, ...)
{
	int sum = 0;

	va_list list;
	va_start(list, n);

	for(int i = 0 ; i < n ; i++)
		sum += va_arg(list, int);
	
	va_end(list);

	return sum;
}

void main()
{
	int s = sum(5, 10, 20, 30, 40, 50);
	printf("s = %d\n", s);
}

~cpp
int func(int a, int b = 10, int c = 30);

~cpp
int abs(int v)
{
	if(v < 0)
		return -v;
	else
		return v;
}

double abs(double v)
{
	if(v < 0.0)
		return -v;
	else
		return v;
}

float abs(float v)
{
	if(v < 0.0F)
		return -v;
	else
		return v;
}

~cpp
#include <stdio.h>

template<typename T>
T abs(T v)
{
	if(v < 0)
		return -v;
	else
		return v;
}

void main()
{
	int a = abs(-10);
	printf("%d\n", a);
}

~cpp
#include <stdio.h>

template<typename T>
T abs(T v)
{
	if(v < 0)
		return -v;
	else
		return v;
}

void main()
{
	double a = abs<double>(-10);
	printf("%f\n", a);
}

~cpp
#include <stdio.h>

template<class T> void print(T a)
{
	printf("not supported\n");
}

template<> void print<const char *>(const char *a)
{
	printf("%s\n", a);
}

template<> void print<int>(int a)
{
	printf("%d\n", a);
}

void main()
{
	print("adfgasg");
	print(121);
	print(0.23);
}

~cpp
#define toupper(a) ((a) >= 'a' && ((a) <= 'z') ? ((a)-('a'-'A')):(a))

vs.

inline char toupper( char a ) {
   return ((a >= 'a' && a <= 'z') ? a-('a'-'A') : a );
}

~cpp
extern "C" void func(int a, int b);

extern "C" {
   void func(int a, int b);
}

~cpp
int (*fp)(int, int, int);