Function reverses numbers in array

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Function reverses numbers in array

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#1 by (4 votes)

1

How does this function work in c that inverts the numbers?

void inverte(int vetor[MAX], int n) {
  int i,aux;

  for (i = 0; i < n/2; i++) {
    // troca posicao i por n-1-i
    aux = vetor[i];
    vetor[i] = vetor[n-1-i];
    vetor[n-1-i] = aux;
  }
  return;
}

I can not understand you.

c array

asked by anonymous 04.03.2016 / 00:58

1 answer

Make calculations based on PHP or MySQL averages Sum of values in Array returns NaN

score 4 · Accepted Answer

I'll take these data as an example:

vetor = 71,72,73,74,75,76,77
n     = 7 (que é o tamanho de "vetor")

So the loop will cause i to go from 0 and stop when it arrives at 7/2 , which is 3 (how i < n/2 was used 3 will not be iterated).

Based on this, see each of the iterations in action, already changing n by 7 , in [n-1-i] and applying i .

These instructions will be executed 3 times, with i being 0 , 1 and 2 :

aux = vetor[i]; vetor[i] = vetor[7-1-i]; vetor[7-1-i] = aux;

Let's apply the loop, with i and [7-1-i] of the 3 iterations in the operations:

i = 0 portanto 7-1-i = 6 -> aux = vetor[0]; vetor[0] = vetor[6]; vetor[6] = aux;
i = 1 portanto 7-1-i = 5 -> aux = vetor[1]; vetor[1] = vetor[5]; vetor[5] = aux;
i = 2 portanto 7-1-i = 4 -> aux = vetor[2]; vetor[2] = vetor[4]; vetor[4] = aux;

Let's replace the right side of the assignments with their values:

i = 0 portanto 7-1-i = 6 -> aux = 71; vetor[0] = 77; vetor[6] = 71;
i = 1 portanto 7-1-i = 5 -> aux = 72; vetor[1] = 76; vetor[5] = 72;
i = 2 portanto 7-1-i = 4 -> aux = 73; vetor[2] = 75; vetor[4] = 73;

So, after executing the 3 steps of the loop:

vetor[0] = 77
vetor[1] = 76
vetor[2] = 75
vetor[3] = 74 (isso nao mudou)
vetor[4] = 73
vetor[5] = 72
vetor[6] = 71