add space after space in char array - c++

Question

So, i need to insert space after space in char string, for example:
we have string: hello world, and function should be return hello world
hello world something else => hello world something else
hello world => hello world (4 spaces) (not necessarily, but preferably)
how?? (definitely need to be used char string)
my solution (it does not work correctly because it insert only 1 space)
from hello world something it returns hello world something:
#include <iostream>
#include <string>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
char* addSpaces(char* str) {
char* p = strchr(str, ' ');
if (p) {
p++;
int n = strlen(p);
p[n + 1] = 0;
while (n) {
p[n] = p[n - 1];
n--;
}
*p = ' ';
}
return str;
}
int main(void) {
const int stringCount = 1;
const int c = 500;
char cstring[stringCount][c];
string str[stringCount];
for (int i = 0; i < stringCount; i++) {
cout << "Enter " << i + 1 << ". line: ";
cin.getline(cstring[i], c);
str[i] = cstring[i];
}
for (int i = 0; i < stringCount; i++) {
cout << "First function result with char in parameter: ";
char* result = addSpaces(cstring[i]);
cout << result << endl;
}
}

Answer 1

Using Dynamic Array:
#include <iostream>
#include <string>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
char *add(char *arr, int lastIndex, char key)
{
int len = sizeof(&arr);
if (len == 0 || arr[len - 1] != '\0')
{
char newArr[len + 100];
newArr[len + 100 - 1] = '\0';
strncpy(newArr, arr, len);
*arr = *newArr;
}
arr[lastIndex] = key;
return arr;
}
int main(void)
{
std::string line;
const int stringCount = 1;
const int c = 500;
cout << "Enter line: ";
std::getline(std::cin, line);
int spaceCount = 0;
char cstring[0];
int lastUpdated = 0;
for (int i = 0; i < sizeof(line); i++)
{
add(cstring, lastUpdated++, line[i]);
if (line[i] == ' ')
{
add(cstring, lastUpdated++, ' ');
}
}
cout << cstring << endl;
}
OR
Check for space first and start char str with len+spaces. and add extra space on each iterate. Else error out of index bound can come.
#include <iostream>
#include <string>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
int main(void)
{
std::string line;
const int stringCount = 1;
const int c = 500;
cout << "Enter line: ";
std::getline(std::cin, line);
cout << line << endl;
int spaceCount = 0;
for (int i = 0; i < sizeof(line); i++)
{
if (line[i] == ' ')
{
spaceCount += 1;
}
}
char cstring[stringCount + spaceCount];
int j = 0;
for (int i = 0; i < sizeof(line); i++)
{
if (line[i] == ' ')
{
cstring[j++] = ' ';
cstring[j++] = ' ';
}
else
{
cstring[j++] = line[i];
}
}
cout << cstring << endl;
}

Answer 2

Modify the main() function according to your needs:
#include <iostream>
#include <cstring>
#include <cstdlib>
#define MAXLEN 500
void add_space(char* str, size_t index, size_t n) {
if (n >= MAXLEN) {
std::cerr << "Cannot further expand the array!" << std::endl;
abort();
}
for (auto i = n; i >= index; --i)
str[i] = str[i - 1];
str[index] = ' ';
}
char* double_spaces(char* str, size_t n) {
for (size_t i = 0; i < n; ++i)
if (str[i] == ' ')
add_space(str, i++, n++);
return str;
}
int main() {
char str[MAXLEN] = "hello world";
std::cout << double_spaces(str, std::strlen(str)) << std::endl;
return 0;
}
Sample Output:
For str[] = "hello world" function returns "hello world"
For str[] = "hello world something else" function returns "hello world something else"
For str[] = "hello world" function returns "hello world"
PS: Better algorithms are possible but they mostly require use of advanced data structures so sticking to the asker's demand of using simple cstrings I have provided one of the simplest and easy to understand solution.
Analysis: The insertion operation requires O(n-index) time which can be reduced by using something similar to ArrayLists.