Script:Reversing a number vector

 This script page was blocked. The script was reviewed and it works perfectly so this page doesn't need anymore editing.

These scripts reverse a number vector in three ways:

1. Using a second vector
2. Without using a second vector
3. Reading it from the keyboard backwards

Variant 1, using a second vector

var v,v2:array[1..50] of integer;
    n,i:integer;
begin
 write ('n='); readln (n);
 for i:=1 to n do
 read (v[i]);
 for i:=n downto 1 do
 v2[n-i+1]:=v[i];
 for i:=1 to n do
 write (v2[i],' ');
 readln;
end.

Explanation

First, we read the vector from the keyboard.

Then, the variable i will travel backwards in the v vector and will assign to the reversed vector v2 at the position n-i+1 the number contained in v[i]. This explains why n-i+1:

n=5;
v=[1, 2, 3, 4, 5];
when i is 5, n-5+1 = 5-5+1 = 0+1=1;
when i is 4, n-4+1 = 5-4+1 = 1+1=2;
when i is 3, n-3+1 = 5-3+1 = 2+1=3;
when i is 2, n-2+1 = 5-2+1 = 3+1=4;
when i is 1, n-1+1 = 5-1+1 = 4+1=5;

Variant 2, without using a second vector

var v:array[1..50] of integer;
    n,i,aux:integer;
begin
 write ('n='); readln (n);
 for i:=1 to n do
 read (v[i]);
 for i:=1 to n div 2 do
 begin
 aux:=v[n-i+1];
 v[n-i+1]:=v[i];
 v[i]:=aux;
 end;
 readln;
end.

Explanation

First, we read the vector from the keyboard. Then, using the auxiliary variable reversing method to replace the reverse the position of the variables in the vector. Here is how it works:

n=10
v=[1,2,3,4,5,6,7,8,9,10] 

The variable i will travel from position 1 to position 10 div 2 = 5 

when i is 1, v[1] will be replaced with v[10] and vice-versa
when i is 2, v[2] will be replaced with v[9] and vice-versa
when i is 3, v[3] will be replaced with v[8] and vice-versa
when i is 4, v[4] will be raplaced with v[7] and vice-versa
when i is 5, v[5] will be replaced with v[6] and vice-versa

The cycle stops here. If the cycle would continue, 
the resulting vector will be the same as the inputed vector 
because the elements would be reversed again.

Variant 3

! This script may be useful only when reading vectors from the keyboard.

var v:array[1..50] of integer;
    n,i:integer;
begin
 write ('n='); readln (n);
 for i:=n downto 1 do
 read (v[i]);
 readln;
end.

Explanation

This script reads the vector backwards. So, if the user inputs 1,2,3,4,5, then 1 will go on the last position and 5 will go on the first position.

See also

• Script:Adding a number range