Stack corruption in message-encoding program [closed] - c++

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I'm trying to write a C++ program that creates a list of letters that will
be used to encode a message according to the following rules:
Input a word
Remove all repeating letters to form the modified word
Place the modified word at the beginning of the array
Fill the remainder of the list with any letters of the alphabet that were not used in the word working from A to Z. (Your list should have all 26 letters of the alphabet)
For example, if the user enters HELLO, the modified word would become HELO, and the list would become HELOABCDFGIJKMNPQRSTUVXYZ. The list must be stored in an array of CHARacters.
This is the code I've written:
#include <iostream>
using namespace std;
int main()
{
char a;
int b = 0;
char word[4] = "\0";
char alphabet[27] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char code[27];
cout << "Please enter a word:" << endl;
cin >> word;
for (int i = 0; i<3; i++)
{
if (word[i] == word[i - 1])
{
a = word[i];
word[i] = word[i + 1];
}
code[i] = word[i];
b++;
}
for (int o = 0; o<27; o++)
{
if (alphabet[o] == word[1] || alphabet[o] == word[2] || alphabet[o] == word[3] || alphabet[o] == word[0])
{
o++;
}
code[b] = alphabet[o];
b++;
}
cout << code;
return 0;
}
Unfortunately, I'm getting this error:
Run-Time Check Failure #2
Stack around the variable word was corrupted.
Secondly, my code works for 4 characters. How can I make it work for any word?

Answer 1

this is a simple way to do this assignment.
note that input word lenght should be smaller than 100
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char word[100]; // input word lenght should be smaller than 100
char used[26];
memset(used, 0, 26);
scanf("%s", word);
for (int i=0; i<strlen(word); i++)
{
// convert to uppercase
if (word[i]>='a' && word[i]<='z')
word[i] -= 'a'-'A';
// skip non-alphabetic characters
if (word[i]<'A' || word[i]>'Z')
continue;
// print this char only if it's not been printed before
if (!used[word[i]-'A'])
printf("%c", word[i]);
// set to 1 so that we don't print it again
used[word[i]-'A'] = 1;
}
// print all unused characters
for (int i=0; i<26; i++)
if (!used[i])
printf("%c", i+'A');
printf("\n");
return 0;
}