Is it possible to know what user write without pressing enter?

Question

I want to check if the user writes something like "car" then I can print "You want to buy it?" or something like that. Is it possible to do that in C?

EDIT: I use Windows. getch() is good but it doesnt show what user writes on the screen. I tried to use putchar()to show them but I cant delete the character on the screen. How do I fix it, or use getch() in my case?

Answer 1

Depending on the system you may use (not always possible) conio - for dos and windows console, ncurses for linux or other related for your system

ncurses - http://www.cs.ukzn.ac.za/~hughm/os/notes/ncurses.html#input

Answer 2

Here is a working example in Windows, as the other answers suggested this is platform dependant.

What I do here is, I've created a function to append a char to a "string". Then I've checked if the keyboard is hit with _kbhit(), if it's hit, I've recorded the value into c variable. Afterwards with our custom function, appended the c variable to str, and checked if first 3 characters of our str is "car" or not.

If it's car, it prints the value you've requested in your question, if user keeps typing, since first 3 characters are now car, it will keep printing the same thing on each key press. You can handle it.

What's the purpose of the counter? It allows you to add a new character to str each loop by making sure that if statement works as intended.

I hope this answer helps you, in the near future, I'll also provide an example for Linux.

Windows

#include <stdio.h>
#include <conio.h>
#include <string.h>

char *append_char(char *sz_string, size_t strsize, char c);

int main()
{
    char str[] = "";
    int counter = 1;
    while (1)
    {
        if (_kbhit()) {
            const char c = _getch();
            append_char(str, sizeof str + counter, c);
            if (strncmp(str, "car", 3) == 0)
            {
                printf("Do you want to buy it?\n");
            }
            counter++;
        }
    }
}

char *append_char(char *sz_string, size_t strsize, char c)
{
    size_t len = strlen(sz_string);
    if ((len + 1) < strsize)
    {
        sz_string[len++] = c;
        sz_string[len] = '\0';
        return sz_string;
    }
    return NULL;
}

Linux

#include <termios.h>
#include <stdio.h>
#include <string.h>

static struct termios old, new;

void initTermios(int echo)
{
    tcgetattr(0, &old);
    new = old;
    new.c_lflag &= ~ICANON;
    if (echo) {
        new.c_lflag |= ECHO;
    }
    else {
        new.c_lflag &= ~ECHO;
    }
    tcsetattr(0, TCSANOW, &new);
}

void resetTermios(void)
{
    tcsetattr(0, TCSANOW, &old);
}

char getch_(int echo)
{
    char ch;
    initTermios(echo);
    ch = getchar();
    resetTermios();
    return ch;
}

char _getch(void)
{
    return getch_(0);
}

char *append_char(char *sz_string, size_t strsize, char c)
{
    size_t len = strlen(sz_string);
    if ((len + 1) < strsize)
    {
        sz_string[len++] = c;
        sz_string[len] = '\0';
        return sz_string;
    }
    return NULL;
}

int main()
{
    char str[] = "";
    int counter = 1;
    while (1)
    {
        const char c = _getch();
        append_char(str, sizeof str + counter, c);
        if (strncmp(str, "car", 3) == 0)
        {
            printf("Do you want to buy it?\n");
        }
        counter++;
    }
}

Answer 3

You can try using getch() in a loop.

getch() is a nonstandard function and is present in conio.h header file which is mostly used by MS-DOS compilers like Turbo C. It is not part of the C standard library or ISO C, nor is it defined by POSIX (Source: http://en.wikipedia.org/wiki/Conio.h) Like above functions, it reads also a single character from keyboard. But it does not use any buffer, so the entered character is immediately returned without waiting for the enter key.

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