Casio fx-3650P - Inverse Calculation - 80 bytes

 Name              Inverse Calculation
 Versions          0.1

 Author            Salvatore Fresta aka Drosophila
 Website           http://www.salvatorefresta.net
 Contact           salvatorefresta [at] gmail [dot] com
 Date              2011-01-15

X. INDEX

 I.    DESCRIPTION
 II.   COMMANDS USED
 III.  CODE
 

I. DESCRIPTION
_______________

Casio fx-3650P is a programmable  scientific  calculator
manufactured by Casio Computer Co., Ltd

In this text I release a software able to calculate  the
inverse of a number in Zn for the Casio fx-3650P.

Usage:

 A: number 1
 B: number 2

 Result: Inverse of A in Z(B)

Inverse:

 C*A = 1 mod B

Return values:

 C (the inverse) on success.
 0 on error.


I. COMMANDS USED
________________

Goto  : Unconditional jump, jump to label.

Lbl   : Label, jump destination.

?     : Operator input command, used when user's input 
        is required.

->    : Assign to variable command, to assign the value
        before it to the variable after it.

=>    : Conditional jump, jump when conditions are met.

>=    : Relational operator.

!=    : Relational operator.

(>)   : Output command, output the value.


http://en.wikipedia.org/wiki/Casio_fx-3650P#Program


III. CODE
_________

The following is the code:

Lbl 0: ?->A: ?->B: 0->C: 0->D: Lbl 1: C+1->C: C>=B => Goto 2: (C*A)/B-.5: Fix 0: Rnd: (C*A-BAns)->D: D!=1 => Goto 1: C (>) Goto 0: Lbl 2: 0 (>) Goto 0


The  following  is a C rappresentation  of  the previous
software:

#include <stdio.h>

void main() {

  int A, B, C, D;

Lbl0:

  printf("\n A: ");
  scanf("%d", &A);

  printf("\n B: ");
  scanf("%d", &B);

  C=D=0;

Lbl1:

  C=C+1;
  if(C >= B) goto Lbl2;

  D = (C*A) % B;
  
  if(D != 1) goto Lbl1;
  
  /* Inverse found successful */
  printf("\n %d\n\n", C);
  goto Lbl0;

Lbl2:

  /* Inverse not found */
  printf("\n 0\n\n");
  goto Lbl0;

}