c++: Problems with my code

Question

#include <iostream>
#include <string>
int main()
{
std::string str;
std::cin >> str;
int count = 0;
int i;
for (i = 0; str[i] != '\0'; ++i) {
count++;
}
if (count % 2 != 0) {
str[i / 2] = ' ';
int n = 0;
for (int j = 0; j <= i; ++j) {
if (str[j] != ' ') {
str[n] = str[j];
n++;
}
}
std::cout << str << std::endl;
}
else {
std::cout << str << std::endl;
}
}

In the above code, in line 15, if I write for (int j = 0; j < i; ++j) instead, the last character will be copied once again. For example, if I input "ab12c", the output will be "ab2cc". However, if I write the same code as the above-for (int j = 0; j <= i; ++j). I can get the output that I want. Why adding a "=" will copy the last character again? Even I am the one who writes this code, I still don't know why.XD

Answer 1

the <= is for less or equal.
what happens when you enter a string with an odd length like 5 for example abcde. is the third char gets replaced by ' '
the string becomes ab' 'de
with < in the loop j gets to 4 because that's less than 5 and never gets to 5,
the str[4] =' e' it gets repeated because j=2 is skipped as it contains ' '.
with <= j will get to 5,the length of the string.
by the end str[5] doesn't contain any char as 5 chars in the str start from 0to4. that's why the last char is not repeated.
I hope it makes sense :)
you can add some std::cout to see the values of the variables at different stages of the executions.
example : std::cout << j << std::endl;
std::cout << str[j] << std::endl;

Answer 2

#include <iostream>
#include <string>
int main()
{
std::string str;
std::cin >> str;
int count = 0;
int i;
for (i = 0; str[i] != '\0'; ++i) {
count++;
}
if (count % 2 != 0) {
str[i / 2] = ' ';
std::cout << str <<std::endl;
int n = 0;
for (int j = 0; j <= i; ++j) {
if (str[j] != ' ') {
str[n] = str[j];
n++;
std::cout << j <<" " << str[j] << std::endl;
}
}
std::cout << str << std::endl;
}
else {
std::cout << str << std::endl;
}
}

Answer 3

OK👌 Thx