Replacing characters from buffer array - c

Question

I am attempting to create a text file and fill it with text, which contains even outer double quotes. Then I want to open this file, give it read-write access, and read the file. After reading the file, iterate over each character and replace those matching a single quote. However, for each match of a single double quote, I either replace it with two backquotes or two single quotes.
However, my attempt was to insert this one index position higher than the matching index for a double quote. This meant I needed to push all characters one step higher.
When given text input like:
//sometext.txt
"some text here"
"read it"
I get:
"some text here"
"read it"``````````````````````````````````````````````````
When using the following:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#define MAX_READ 50
int main(){
int fd;
fd = open("test.txt", O_RDWR);
if (fd == -1){
printf("Failed");
exit(EXIT_FAILURE);
}
char buffer[MAX_READ+1];
ssize_t numRead;
numRead = read(fd, buffer, MAX_READ);
if (numRead == -1){
printf("Failed");
exit(EXIT_FAILURE);
}
buffer[numRead] = '\0';
int j = 1;
size_t chars = sizeof(buffer)/sizeof(buffer[0]);
for(int i = 0; i < chars; i++){
if(buffer[i] == '"'){
if(j % 2 != 0){
buffer[i] = '`';
chars++;
while(i < chars){
i++;
buffer[i] = buffer[i-1];
}
}else{
buffer[i] = '\'';
chars++;
while(i < chars){
i++;
buffer[i] = buffer[i-1];
}
}
j++;
}
printf("\nString characters: %c", buffer[i]);
}
ssize_t numWrite;
numWrite = write(fd, buffer, MAX_READ);
if (numWrite == -1){
printf("Failed");
exit(EXIT_FAILURE);
}
return 0;
}
Expected output:
``some text here''
``read it''