C-Code

/****************************************
  * prod2.c    Produkt ohne Multiplikation
  *            Dezimale Stellenwertaddition
  *            ("schriftlich multiplizieren")
  *
  * OS     :   GNU/Linux
  * compile:   gcc -Wall -o prod prod2.c
  *
  * devnull    08-07-2013
  ****************************************/
#include <stdlib.h>
#include <limits.h>
#include <values.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>

/* return an unsigned int */
unsigned int get_number( int lfn )
{
	char snum[20];
	char *ep;
	long int lnum;
        
	while (1) {
		printf(" %d. positive ganze Zahl: ", lfn );
        scanf( "%s", snum );
            
        errno = 0;
        lnum = strtol( snum, &ep, 10);
		if ((errno==0) && (*ep=='\0')) {
			if (lnum>=0 && lnum<=INT_MAX) 
				break;
			printf( "Zahl liegt ausserhalb Limits (0..%d)!\n",INT_MAX );
		}
		else
			printf( "Eingabe hat kein korrektes 'long int'-Format!\n" );
	}
	return (unsigned int)lnum;
}

/* calculate x*cdigit w/o multiplication */
unsigned long int mul( unsigned long int x, char cdigit )
{
	switch (cdigit) {
	 case '1': return x;
	 case '2': return x<<1;
	 case '3': return (x<<1)+x;
	 case '4': return x<<2;
	 case '5': return (x<<2)+x;
	 case '6': return ((x<<1)+x)<<1;
	 case '7': return (((x<<1)+x)<<1)+x;
	 case '8': return x<<3;
	 case '9': return (x<<3)+x;
	 case 'A': return ((x<<2)+x)<<1;
	}
	return 0;
}

unsigned long int prod( unsigned int i1, unsigned int i2 )
{
	unsigned long int sum=0;
    unsigned long int l1=0;
	char istr[12];
	int p;
	
    l1=(unsigned long int)i1; 		
    sprintf( istr, "%u", i2 );
    for (p=strlen(istr);p;p--) {
		sum += mul(l1,istr[p-1]);
		l1 = mul(l1,'A');
	}
	return sum;
}

/* main */
int main( void )
{
	unsigned int a = get_number(1);
	unsigned int b = get_number(2);
	printf("%u x %u = %lu\n",a,b,prod(a,b));
    return 0;
}