About passing by reference and by value

Question

I can’t understand when to use one or the other. in this code, I used both forms and saw no change at the end. What’s the difference and when to use one or the other

Create a procedure that receives two values per reference and sort them in ascending order. Create a main algorithm to call the procedure and display values after ordering.

Algoritmo "procedimento"

Var
 x, y: inteiro

   Procedimento crescente(var A,B: inteiro)
   var
   cres: inteiro
   inicio

   Se (a < b) entao
         para cres de a ate b faca
            Escreva(cres)
            cres <- cres + 1
         fimpara
      Senao
        para cres de b ate a faca
             Escreva(cres)
             cres <- cres + 1
        fimpara
      Fimse

   FimProcedimento

Inicio

  x <- 10
  y <- 20


  crescente(x, y)

Fimalgoritmo

Answer 1

I made a little adjustments to your program. Don’t be sad with me! : )

I tried to explain as best I could!

Algorithm "procedure"

Inicio

    Var x, y: inteiro

    x <- 10 
    y <- 20

    crescente(x, y) 

    escreva(x)
    escreva(y)

Fim 

/* 
  Comentario:
    Neste procedimento o primeiro parâmetro A é passagem por referência, porque precede de var, 
                           então o valor de A será alterado mudando o valor de x.
                       o segundo parâmetro B é passagem por valor, 
                           então o valor de B será alterado SOMENTE dentro do procedimento e não vai alterar o valor de y.
*/ 
Procedimento crescente(var A, B: inteiro) 

  inicio
        Se (A < B) entao 
            para A ate B faca 
                Escreva(A) 
                A <- A + 1 
            fim-para
        Senao
             para B ate A faca 
                Escreva(B) 
                B <- B + 1 
             fim-para
        fim-se
   fim

Fim-Procedimento

Endpoint

Let’s run your program:

X = 10 (Initial value) Y = 20 (Initial value)

made the procedure call: increasing(10,20)

running within the growing procedure:

A = 10 B = 20

As 10 is less than 20 will enter the first condition (If (A < B)). Then it will perform the repeat loop (for) will run from 10 to 20 and ends the repeat structure.

A = 10 displays 10 A = 11 displays 11 ... A=20

out of the growing procedure.

I added two commands write to x and y after the growing procedure.

displays 20 (x end value) displays 20 (y end value)

Good programming practice is to make a good indentation of your code to make clear the understanding of the code and helps a lot in maintenance (possible changes that need to be made).

[visualg]