C Program for Multiplication Of Large Integer Using Divide And Conquer

#include< stdio.h >
#include< conio.h >
#include< math.h >
long prod(long,long);

long noOfDigit(long,long);
void main()
{
 long m,n;
 clrscr();
 printf("\n-----------------------------------------------");
 printf("\nMULTIPLICATION USING DIVIDE & CONQUER");
 printf("\n-----------------------------------------------");
 printf("\n Enter number1:");
 scanf("%ld",&m);
 printf("\n Enter number2:");
 scanf("%ld",&n);
 printf("\n-----------------------------------------------");
 printf("\n multiplication of %ld and %ld is:%ld",m,n,prod(m,n));
 printf("\n-----------------------------------------------");
getch();
}

long prod(long u,long v)
{
 long x,y,w,z;
 long n,m,p,q,r;

 n=noOfDigit(u,v);

 if(u==0 || v==0)
 {
  return 0;
 }


 else if(n<=2)
 {
  return (u*v);
 }
 else
 {
  m=floor(n/2);

  w=u/pow(10,m);
  x=u%(int)pow(10,m);
  y=v/pow(10,m);
  z=v%(int)pow(10,m);

  p=prod(w,y);
  q=prod(x,z);
  r=prod(w+x,y+z);

  return p * pow(10,2*m) + (r-p-q) * pow(10,m) + q;
 }
}


long noOfDigit(long m,long n)
{
 long max;
 int b=0;
 if(m>=n)
  max=m;
 else
  max=n;
 while(max>0)
 {
  max=max/10;
  b++;
 }
 return b;
}


OUTPUT


-----------------------------------------------
MULTIPLICATION USING DIVIDE & CONQUER
-----------------------------------------------
 Enter number1:1234

 Enter number2:7654

-----------------------------------------------
 multiplication of 1234 and 7654 is:9445036
-----------------------------------------------