Avoid pressing enter with getch() on Linux ( GCC ) "No-echo" - c

Question

In the next code: I don't have to press Enter to get the character with getch() and this is only applicable on Windows (mingw) . I am programming a simple stopwatch which reacts if a keyboard-key is pressed without the need to press ENTER, but the same thing doesn't work on Linux ( GCC ). And I have to find a solution only using getch() with no echo. I've been Googling around with no luck. Thank you in advance.
PS: I am a c/c++ beginner.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main(void) {
printf("\n\t\tStopwatch \n\n \t Press S to start \n\n");
time_t start;
char c ;
struct tm tm ;
do {
c=getch(); /*get the Character without pressing ENTER*/
if (c!= 'S' && c!= 's') printf("\nWrong key. Please press'S' to Start\n");
} while(c!= 'S' && c!= 's');
start=time(NULL);
tm = *localtime(&start);
printf("\n Starting time :: %d:%d:%d \n", tm.tm_hour, tm.tm_min, tm.tm_sec);
return 0;
}

Answer 1

Unix (and so Linux) have a concept of terminal (TTY) which can be pretty complicated.
Every process can be associated with a terminal (and lot actually are).
This terminal has different options like the ECHO you mentioned and the LINE BUFFER (which is the enter problem which you reported).
To set a terminal the low level APIs are termios (see "man termios").
Another more friendly API is ncurses (see "man ncurses"). For instance at https://www.mkssoftware.com/docs/man3/curs_inopts.3.asp you can see some function for different settings.
An easy example with ncurses (you can compile with "gcc -O2 source.c -o output -lncurses"):
#include <stdio.h>
#include <ncurses.h>
int main(void)
{
initscr();
cbreak();
noecho();
int n = getch();
printf("%d %c\n", n, n);
}