How to write Console terminal with C++ [closed] - c++

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I am studying for an exam and need your help.
I must write my own console terminal in C++, which must work in this way:
Example:
:>plus 5 7 "hit ENTER"
:>12
:>minus 10 12 "hit ENTER"
:>-2
:>combine Hello World "hit ENTER"
:>HelloWorld
:>run netstat "hit ENTER"
:>runs netstat
:>help
:>plus int1 int2
minus int1 int2
combine string1 string2
run ?????
:>exit
program exits
For main block I think it would be something like this
int main(void) {
string x;
while (true) {
getline(cin, x);
detect_command(x);
}
return 0;
}
The functions would be something like this
void my_plus(int a, int b) {
cout << a + b;
}
void my_minus(int a, int b) {
cout << a - b;
}
void my_combine(string a, string b) {
?????????????;
}
void my_run(?????????) {
???????????;
}
And the finally detect_command
void detect_command(string a) {
const int arr_length = 10;
string commands[arr_length] = { "plus", "minus", "help", "exit" };
for (int i = 0; i < arr_length; i++) {
if (a.compare(0, commands[i].length(), commands[i]) == 0) {
?????????????????????;
}
}
}
????? - means I don`t know what to write.
Help to make this program work.
Thanks.

Answer 1

I'm going to use the minus operation as an example...
Make a structure like so:
struct cmd_struct {
const char *name;
void (*func) (void *data);
};
Since your function parameters aren't the same, you gotta make a structure for each, e.g.:
struct minus_op {
int rhs;
int lhs;
};
And use the cmd_struct as an array, like so:
static cmd_struct commands[] = {
{ "minus", &my_minus },
...
};
my_minus would then be:
void my_minus(void *data) {
struct minus_op *mop = data;
... do the computation and return ...
}
And loop through it to detect the command used:
for (int i = 0; i < sizeof(commands) / sizeof(commands[0]); ++i) {
if (strcmp(commands[i].name, a) == 0) {
... prepare the data ...
commands[i].func(data);
}
}
Side Note: In order to get the function parameters from command line, have a splitter, e.g. a white space. Use a vector for this and pass that vector to detect_command
Do also note: Get rid of the void param used in this example and use a char **argv and int argc like in main(). argv would be the arguments, and argc would be the number of arguments passed to the function. e.g. if you say to the program:
>> minus 5 1
Then argc should be 2 (the 5 and the 1) and argv[0] = "5" and argv[1] = "1".
Now that you know the idea behind it, implementing a more flexible version is left to you.

Answer 2

Call a respective function to handle each word. For example:
enum commands {
PLUS,
MINUS,
HELP,
EXIT
//....
};
int detect_command(string a) {
const int arr_length = 10;
string commands[arr_length] = { "plus", "minus", "help", "exit" };
for (int i = 0; i < arr_length; i++) {
if (a.compare(0, commands[i].length(), commands[i]) == 0)
return i;
}
return -1; //unknow word
}
Give the string to detect_command() the function return the respective integer to enum commands (that's our i value) or -1 if word is unknow. Then you can write a function like this to use and process the value determined by detect_command():
void run_command(int cmd)
{
switch(cmd) {
case PLUS: run_plus(); break;
case MINUS: run_minus(); break;
// and so on to all comamnds available
default: error("unknow command");
}
}
each function run_*() should continues the command parsing according to own rules, i.e, the "plus" command should be follow by one integer, one white-space and then another integer, right? run_plus() must validate it and then compute the result. e.g.:
//pseudo code
void run_plus()
{
//input here is one after "plus" word
//here we must validate our valid input: two digits split by a white-spaces
int x = parse_digit();
check(white-space);
int y = parse_digit();
int r = x + y;
display_result(r);
}
NOTE: I'm not a C++ programmer; I did detect_command() code modification to you get my idea. I even don't know if it will compile in C++ for the mismatch types.