#include<stdio.h>
#include<conio.h>


float deQuy(int n) // đệ quy
{
	if(n == 1)
		return 0.5;
	return deQuy(n - 1) + 1.0 / (2 * n);
}

float deQuyDuoi(int n, float x = 0.5)  // đệ quy đuôi
{
	if(n == 1)
		return x;
	return deQuyDuoi(n - 1, x +  1.0 / (2 * n));
}

float khuDeQuy(int n) // khử đệ quy
{
	float S = 0;

	for(int i = 1; i <= n; i++)
	{
		S = S + 1.0 / (2 * i);
	}
	return S;
}
int main()
{
	int n;
	printf("\nNhap n: "); scanf("%d", &n);

	
	printf("\nDe quy(%d) = %f", n, deQuy(n));
	printf("\nDe quy duoi(%d) = %f", n, deQuyDuoi(n));
	printf("\nKhu de quy(%d) = %f", n, khuDeQuy(n));

	
	 
	getch();
	return 0;
}

Line 17: error: conio.h: No such file or directory
Line 12: error: expected ';', ',' or ')' before '=' token
In function 'khuDeQuy':
Line 23: error: 'for' loop initial declaration used outside C99 mode