What happens to variable i in this algorithm? Sequence inversion algorithm

Question

Good evening. I started to study data structure in support of the book Data Structure and Algorithms 2nd ed (SZWARCFITER/MARKENZON). The first algorithm of the book deals with reversing the elements of the sequence in the vector, exchanging the position of the last element with the first, successively until the last element. The algorithm is this:

algoritmo 1.1: Inversão de uma sequencia
   para i <- 1...[n/2] faça
       temp <- S[i]
       S[i] <- S[n - i + 1]
       S[n -i + 1] <- temp

I wrote the algorithm on Portugol and added an excerpt that completes the list.

var


S:VETOR[1..10] de INTEIRO
  i,j,temp,t: INTEIRO
inicio

para i de 1 ate 10 faca
     S[i] <- i
fimpara

para i de 1 ate 10 faca
     escreva(S[i], " ")
fimpara

 Escreval(" ")

 para j de 1 ate 10 faca
      temp <- S[j]
      S[j] <- S[10-j+1]
      t <- S[10-j+1]
      se (j>5) entao
              S[j] <- -j+i
              t <- -j+i
      fimse
      escreva(t, " ")
 fimpara

fimalgoritmo

My question is about the variable i. Why does it assume the value 11 after printing the list? Before arriving at this code, I used an auxiliary variable k, to list the numbers smaller than 6 in reverse order, but I realized that i assumed the value 11, so I started doing -j+i. Somebody explain this to me?

Answer 1

Look at what I know of algorithm, portugol and everything else, if you start at 0 or 1 or 2 whatever, what matters is that you know what you’re doing, going on, what you can do is the following: at the time you will assign the values of i in another vector, while you assign the inverse already assigns again, it mounted on the main vector.

I’ll try to explain with an example:

funcao inversao():inteiro
var
inversor :vetor [0..9] de inteiro // vetor inversor
contador_inversor:inteiro
inicio
escreval (" A ORDEM INVERSA É: ")
contador <- 10
para contador_inversor de 0 ate 12 faca
     inversor[contador_inversor] <- c[contador]
     contador <- contador - 1
fimpara
para contador de 0 ate 12 faca
     c[contador] <- inversor[contador]
     escreva(" ", c[contador])
fimpara
escreval(" ")
fimfuncao

I give you this example to take as a basis, because it is of a project that I did, if it did not serve me tell me that I help you better, but try to interpret from this that works for me here.