/*********************************************
* This program converts a number in base a   *
* into a number in base b (a and b must be   *
* between 2 and 36).                         * 
* ------------------------------------------ *
* Ref.: "Mathématiques en Turbo-Pascal By    *
*        M. Ducamp and A. Reverchon (2),     *
*        Eyrolles, Paris, 1988" [BIBLI 05].  *
* ------------------------------------------ *
* Sample runs:                               *
*                                            *
* BASE CONVERSION                            *
*                                            *
* Start  Base (2 to 36): 5                   *
* Arrival Base (2 to 36): 3                  *
*                                            *
* Enter number in start base: 3421           *
* In base 3: 200000                          *
* Enter number in start base: 3420           *
* In base 3: 122222                          *
*                                            *
*                                            *
* BASE CONVERSION                            *
*                                            *
* Start  Base (2 to 36): 10                  *
* Arrival Base (2 to 36): 16                 *
*                                            *
* Enter number in start base: 65535          *
* In base 3: FFFF                            *
* Enter number in start base: 100            *
* In base 3: 64                              *
*                                            *
* BASE CONVERSION                            *
*                                            *
* Start  Base (2 to 36): 16                  *
* Arrival Base (2 to 36): 2                  *
*                                            *
* Enter number in start base: FF             *
* In base 3: 11111111                        *
* Enter number in start base: 3A             *
* In base 3: 111010                          *
* Enter number in start base: E2             *
* In base 3: 11100010                        *
*                                            *
* Note: Enter 0 to exit.                     *
*                                            *
*                 C++ version by J-P Moreau  *
*                     (www.jpmoreau.fr)      *
**********************************************
Explanations:
------------
The letters A,B,...,Z  represent 10,11,...,36
in the base > 10.

The number is first converted from base a to
base 10 by Function DecodeBase, then  converted
from base 10 to base b by Function CodeBase.   */

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <math.h> 

#define  MAXREAL  1e40
#define  FALSE    0
#define  TRUE     1

int   ba,bd;
char  x[40],y[40];
float r;

//Convert a number from base b to base 10. The function returns
//FALSE if b not in [2..36] or if string x contains invalid
//characters in base b or if result y is too big.
bool DecodeBase(char *x,int b, float *y) {
  int lgth,i,j;
  float mult; char *ch;
  if (b<2 || b>36) {
    printf(" Base must be between 2 and 36 !\n");
    return FALSE;
  }
  *y=0; mult=1.0;
  lgth=strlen(x);
  for (i=0; i<lgth; i++) {
    ch=&x[lgth-i-1];
    if (!isalnum(ch[0])) {
	  printf(" Error in input number.\n"); 
	  return FALSE;
    }
    if (*ch<='9')
	  j=toupper(*ch)-'0';
    else 
      j=toupper(*ch)-'A'+10;
    if (j>=b) return FALSE;
    *y+=mult*j;
    if (mult>MAXREAL/b) return FALSE;
    mult=mult*b;
  }
  return TRUE;
}

//Convert a number from base 10 to base b. The function returns
//FALSE if b not in [2..36] or if string x contains invalid
//characters in base 10 or if number x is too big.
bool CodeBase(float x,int b, char *y) {
  int n; char ch[2];
  if (b<2 || b>36) {
    printf(" Base must be between 2 and 36 !\n");
    return FALSE;
  }
  strcpy(y,"");
  while (x>0) {
    n=(int) floor(x-b*int(x/b));
    if (n<10) {
      //y=Chr(Ord("0")+n)+y;
      sprintf(ch,"%d",n);
	  strcat(y,ch);
    }
    else { 
      //y=Chr(Ord("A")+n-10) +y;
      switch(n) {
	    case 10: strcat(y,"A"); break;
        case 11: strcat(y,"B"); break;
	    case 12: strcat(y,"C"); break;
        case 13: strcat(y,"D"); break;
	    case 14: strcat(y,"E"); break;
        case 15: strcat(y,"F"); break;
	    case 16: strcat(y,"G"); break;
        case 17: strcat(y,"H"); break;
	    case 18: strcat(y,"I"); break;
        case 19: strcat(y,"J"); break;
	    case 20: strcat(y,"K"); break;
        case 21: strcat(y,"L"); break;
	    case 22: strcat(y,"M"); break;
        case 23: strcat(y,"N"); break;
	    case 24: strcat(y,"O"); break;
        case 25: strcat(y,"P"); break;
	    case 26: strcat(y,"Q"); break;
        case 27: strcat(y,"R"); break;
	    case 28: strcat(y,"S"); break;
        case 29: strcat(y,"T"); break;
	    case 30: strcat(y,"U"); break;
        case 31: strcat(y,"V"); break;
	    case 32: strcat(y,"W"); break;
        case 33: strcat(y,"X"); break;
	    case 34: strcat(y,"Y"); break;
        case 35: strcat(y,"Z");
	  }
    }
    x=(float) int(x/b);           
  }
  y=strrev(y); //string inversion
  return TRUE;
}

void main()  {
  printf("\n BASE CONVERSION\n\n");
  printf(" Start  Base (2 to 36): "); scanf("%d",&bd);
  printf(" Arrival Base (2 to 36): "); scanf("%d",&ba);
  strcpy(x,"1");
  while (strcmp(x,"0")!=0) {
    printf("\n Enter number in start base: "); scanf("%s",x);
    if (strcmp(x,"0")!=0) {
      if (DecodeBase(x,bd,&r)) {
        if (CodeBase(r,ba,y))
          printf(" In base %d:  %s\n",ba,y);
        else
          printf(" Error in coding number.\n");
      }
      else
        printf(" Error in decoding number.\n");
    }
  }
  printf("\n\n");
}

//end of file basis.cpp