Bài 1:
//dem so chu so cua so nguyen duong n nhap tu ban phim
#include <stdio.h>
void nhap (int &n);
int xuLy (int n);
void xuat (int kq);
void main ()
{
	int n;
	nhap (n);
	int kq=xuLy(n);
	xuat (kq);
}
void nhap (int &n)
{
	scanf ("%d",&n);
}
int xuLy (int n)
{
	int s=1;
	if (n==0)
	{
		return s;
	} else
	{
		while ((n/10)!=0)
		{
			s=s+1;
			n/=10;
		}
		return s;
	}
}
void xuat (int kq)
{
	printf ("%d",kq);
}
Bài 2 :
// minh hoa cho chuong trinh input 123 output 1 2 3
#include <stdio.h>
#include <math.h>
void nhap (int &n);
int dem (int n);
void xuat (int soLuong, int n);
void main ()
{
	int n;
	nhap (n);
	int soLuong=dem (n);
	xuat (soLuong,n);
}
void nhap (int &n)
{
	scanf ("%d",&n);
}
int dem (int n)
{
	int s=1;
	if (n==0)
	{
		return s;
	} else
	{
		while ((n/10)!=0)
		{
			s=s+1;
			n/=10;
		}
		return s;
	}
}
void xuat (int soLuong, int n)
{
	int phu=soLuong-1;
	for (phu;phu>=0;phu--)
	{
		int so=(n/ int (pow (10,phu)));
		printf ("%d ",so);
		n=n%(int(pow(10,phu)));
	}
}
Bài 3:
//tinh tong cac phan tu co trong so n nguyen duong duoc nhap tu ban phim
#include <stdio.h>
#include <math.h>
void nhap (int &n);
int dem (int n);
int tinhTong (int soLuong, int n);
void xuat (int kq);
void main ()
{
	int n;
	nhap (n);
	int soLuong=dem (n);
	int kq=tinhTong (soLuong,n);
	xuat (kq);
}
void nhap (int &n)
{
	scanf ("%d",&n);
}
int dem (int n)
{
	int s=1;
	if (n==0)
	{
		return s;
	} else
	{
		while ((n/10)!=0)
		{
			s=s+1;
			n/=10;
		}
		return s;
	}
}
int tinhTong (int soLuong, int n)
{
	int tong=0;
	int phu=soLuong-1;
	for (phu;phu>=0;phu--)
	{
		int so=(n/ int (pow (10,phu)));
		tong=tong+so;
		n=n%(int(pow(10,phu)));
	}
	return tong;
}
void xuat (int kq)
{
	printf ("%d",kq);
}
Bài 4:
//ghep so
#include <stdio.h>
#include <math.h>
void nhap (int &a, int &b);
int dem (int n);
int tinhTong (int soLuong, int a,int b);
void xuat (int kq);
void main ()
{
	int a,b;
	nhap (a,b);
	int soLuong =dem(b);
	int kq=tinhTong(soLuong,a,b);
	xuat (kq);
}
void nhap (int &a, int &b)
{
	scanf ("%d%d",&a,&b);
}
int dem (int n)
{	int s=1;
	int soLuong=1;
	if (n==0)
	{
		return s;
	} else
	{
		while ((n/10)!=0)
		{
			soLuong=soLuong+1;
			n/=10;
		}
		return soLuong;
	}
}
int tinhTong (int soLuong, int a,int b)
{
	int tong=a*int (pow(10,soLuong));

	return (tong +b);
}
void xuat (int kq)
{
	printf ("%d",kq);
}