CODEWITHSUNDEEP
stringluareverse
user2793250
user2793250

Reputation: 21

How to reverse a string?

I do not want to use string.reverse() instead I want to create my own way. But I am failing. Where did I go wrong:

function wait(n)
  local now = os.time()
    while  os.time() - now < n do end
end

sit = "1234 1234"

function revers(sit)
 wait(1)
  local table = { " nil "}
    print(#sit, os.date("%M"))
      while #table < #sit do
        table.insert(table, #table+1, sit:find(".", #sit))
         print(#table, #sit)
          wait(1)
 end
 end

 revers(sit)

Upvotes: 1

Views: 1141

Answers (4)

zKaj
zKaj

Reputation: 9

This copies array a value "Wednesday" to array b in reverse order.

#include <stdio.h>
main()
{
char a[] = "Wednesday";
char b[12];
char *a_ptr, *b_ptr;

int lkm = 0;    /* number of characters */

int i = 0;
while(a[i] != '\0')
    {
    i++;
    lkm++;
    }

lkm = lkm - 1; 

a_ptr = a;
b_ptr = b;
a_ptr += lkm;

int j;
for(j = lkm; j >= 0; j--)
    {
    *b_ptr = *a_ptr;
    a_ptr--;
    b_ptr++;
    }

fprintf(stdout, "Before: %s\n", a);
fprintf(stdout, "After:  %s\n", b);
return(0);
}

Program output:
Before: Wednesday
After:     yadsendeW

Upvotes: -1

Seg Fault
Seg Fault

Reputation: 1351

Sorry to say, but your code has some fundamental issues:

  • The function revers does not return anything
  • The function revers only attempts to build a table, not a string
  • Tables in Lua can't contain nil, either as key or as value
  • The sit:find(".",#sit) uses the wrong, constant starting point for the find
  • ...
  • Put together it doesn't even come close to reverse the string

Try to understand the following code that should do the job:

function revers(s)
  local r = ""
  for i = 1,#s,1 do
    r = s:sub(i,i) .. r
  end
  return r
end

Upvotes: 3

Marko Gresak
Marko Gresak

Reputation: 8207

You should just try to loop through each character in sit and write it to a table. Try using this instead of your while loop

for c in str:gmatch"." do
    table.insert(table,c)
    -- or
    table = table .. c  -- the table shouldn't be initialized nil in this case
end

Upvotes: 0

Erik Nedwidek
Erik Nedwidek

Reputation: 6184

The issue is 

local table = { " nil " }

You can't name a variable after a reserved word. If you change it to

local mytable = { " nil " }

Also change all subsequent uses like so:

function wait(n)
  local now = os.time()
    while  os.time() - now < n do end
end

sit = "1234 1234"

function revers(sit)
 wait(1)
  local mytable = { " nil "}
    print(#sit, os.date("%M"))
      while #mytable < #sit do
        mytable.insert(mytable, #mytable+1, sit:find(".", #sit))
         print(#mytable, #sit)
          wait(1)
 end
 end

 revers(sit)

A simpler way to do this though is:

function revers(sit)
  local mytable = { " nil "}
  for i = 0, #sit+1 do
    table.insert(mytable, string.sub(sit, #sit-i, #sit-i))
  end
end

The table now contains an array of the string characters in reverse order.

Upvotes: 0

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