(m!+n!)/(m+n)!

int m,n;
int M=1,N=1,MN=1;
printf("nhap m va n :");
scanf("%d %d",&m &n);
//tinh m!
for ( int i = 1 ; i <=m ; i++ )
	M=M*i;
//tinh n!
for ( int i = 1 ; i <=n ; i++ )
	N=N*i;
//tinh (m+n)!
for ( int i = 1 ; i <= (m+n) ; i++ )
	MN=MN*i;
printf("ket qua la : %f",(M+N)/MN);
getch();