UVa 389 - Basically Speaking

#include <iostream>
#include <cstdlib>
#include <cstdio>

using namespace std;

char buf[36];

int change1( char c )
{
	if ( c >= '0' && c <= '9' )
		return c - '0';
	return c - 'A' + 10;
}

int change2( char c )
{
	if ( c < 10 )
		return c + '0';
	return c - 10 + 'A';
}

int main()
{
	int base1,base2;
	while ( scanf("%s%d%d",buf,&base1,&base2) != EOF ) {
		int value = 0,move = 0,save = 0;
		while ( buf[move] ) {
			value *= base1;
			value += change1(buf[move ++]);
		}
		if ( !value ) buf[save ++] = '0';
		while ( value ) {
			buf[save ++] = change2(value%base2);
			value /= base2;
		}
		if ( save > 7 ) printf("  ERROR\n");
		else {
			for ( int i = save ; i < 7 ; ++ i )
				printf(" ");
			while ( -- save >= 0 )
				printf("%c",buf[save]);
			printf("\n");
		}
	}
	return 0;
}