Replace one character with multiple characters - c

Question

I need to replace " " (space) with ", " (comma and space).
I have function which receive string as char* and after replacing all this characters prints string on screen.
char* PrintComma(char* Text) {
for (int i = 0; i < strlen(Text); i++) {
if (Text[i] == ' ') {
Text[i] = ',';
}
}
return Text;
}
This replaces " " with "," but I need ", ". I'm not allowed to use a second string or array for saving temp data. I can use only this one string.
Example:
Input => "Hello world my name is"
Output => "Hello, world, my, name, is"

Answer 1

This problem seems like a perfect setup for memmove() which is a library function that copies bytes between two strings but handles overlapping memory blocks.
memmove(
char_pointer + make_room_at + room_to_make,
char_pointer + make_room_at,
init_size - make_room_at + room_to_make
);
Here is the application using memmove().
char* PrintComma(char* Text) {
for (int i = 0; i < strlen(Text); i++) {
if (Text[i] == ' ') {
memmove(
Text + i + 1,
Text + i,
strlen(Text) - i + 1
);
Text[i++] = ',';
}
}
return Text;
}

Answer 2

Here's a working example. The input buffer must be large enough to store the replaced string, as the requirements state that no new string should be created.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void PrintComma(char* Text)
{
char* str = Text;
size_t c, len = strlen(Text);
for (c = 0; Text[c]; Text[c] == ' ' ? c++ : *Text++);
for (size_t i = 0; i < len + c; i++)
{
if (str[i] == ' ')
{
str[i] = ',';
char last = ' ';
for(size_t u = i + 1; u < len + c; u++)
{
char current = str[u];
str[u] = last;
last = current;
}
i += 2;
}
}
}
int main(void)
{
char tmp[100] = { 0 };
const char* TEST = "Hello world my name is";
memcpy(tmp, TEST, strlen(TEST));
printf("Input: %s\n", tmp);
PrintComma(tmp);
printf("Output: %s\n", tmp);
return 0;
}
Result:
Input: Hello world my name is
Output: Hello, world, my, name, is

Answer 3

Based on your requirements:
I have function which receive string as char* and after replacing all this characters prints string on screen.
I don't think you're looking to replace a space with a comma-space. Instead, I think you want to go through the string and print all the characters. When you encounter a space, you print an extra comma. Here's roughly how to do that:
void PrintComma(char *text)
{
const size_t len = strlen(text); // don't call on every iteration
for(size_t i = 0; i < len; i++)
{
if(text[i] == ' ')
putchar(',');
putchar(text[i]);
}
}

Answer 4

You have two requirements:
1) The spaces must be replaced.
2) You cannot use another char array.
These lead to the assumption that the input char* must have adequate allocated space for all the new ,s.
In that case, this would work.
char *PrintComma(char *Text) {
int numberOfSpaces = 0, orignalLength = strlen(Text);
for (int i = 0; i < strlen(Text); i++) {
if (Text[i] == ' ')
numberOfSpaces++;
}
for (int i = orignalLength - 1, j = orignalLength + numberOfSpaces - 1; i >= 0; i--) {
Text[j] = Text[i];
j--;
if (Text[i] == ' ') {
Text[j] = ',';
j--;
}
}
return Text;
}