Category: C / C++

As a test, I was asked to write a morse code task where some of the signals weren’t able to be determined from the input. So in this case instead of having either the dot (.) or dash (-) we have a question mark (?) where it could be either a dot / dash.

Here is an image of the morse code alphabet of dots / dashes and here is a link to a view of the “tree” of the morse code of the dichotomic search, basically binary search of the morse code.

So, we are only going down 3 levels, below are some tests to confirm that the process is working fine.

class item {
    private:
        char value;
        item *left;
        item *right;
    public:
        item(char value,item *left,item *right);
        item(char value);
        item(item *left,item *right);

        item();

        char getValue();

        item* leftItem();
        item* rightItem();
};

    item* head = new item(
        new item('e',
            new item('i', 
                new item('s'),
                new item('u')
            ),
            new item('a',
                new item('r'),
                new item('w')
            )
        ),
        new item('t',
            new item('n', 
                new item('d'),
                new item('k')
            ),
            new item('m',
                new item('g'),
                new item('o')
            )
        )
    );

string output(string signal, item* codes) {
    string ret="";
    if (signal.size() ==0 ) 
        return string(1,codes->getValue());
    for (string::size_type i=0; i < signal.size();i++) {
        if ('?' == signal[i]) {
            ret += output("."+signal.substr(i+1),codes);
            ret += output("-"+signal.substr(i+1),codes);
            return ret;
        } else if ('.' == signal[i]) {
            return output(signal.substr(i+1),codes->leftItem());
        } else if ('-' == signal[i]) {
            return output(signal.substr(i+1),codes->rightItem());
        } else {
            throw invalid_argument(string("Invalid character at this point of the string ").append(signal));
        }
    }
    return ret;
}

If you want to view the whole code, here is the link to the zip file of the morse code.

A friend of mine asked how to use the newer for_each and is it similar to the foreach in php, so here is the example that I gave and thus doing it online as well.

To start with the foreach (php version here) does loop over data and so does the for_each in c++, but the main difference is that the for_each in c++ is basically a for loop

for (; first!=last;++first)
   functionCall(*first);

where the functionCall is the parameter passed in to do something with that part of the data.

The great thing with c++ is that you are able to use either a method, structure etc as long as it is able to output a variable then we are good.

So here is a example, please note that I am loading up a vector e.g. only functions that have a single int make sense.

void printNumber (int i) {
	cout << "Print the number from a function : " << i << "\n";
}
 
for_each(v.begin(), v.end(), printNumber);

here we are using the for_each (where the v is a vector) passing in the start and end of the vector with a function as the last parameter.

and here

// create a object that can use the operator() to output value passed in.
struct structToOutput {
	void operator() (int i) {
		cout << "Struct to output : " << i << "\n";
	}
} structToOutputObject;
 
for_each(v.begin(), v.end(), structToOutputObject);

will output the values differently but in essence still able to access the values.

Here is the code in full

#include <iostream>
#include <vector>
#include <algorithm>
 
using namespace std;
 
void printNumber (int i) {
	cout << "Print the number from a function : " << i << "\n";
}
 
// create a object that can use the operator() to output value passed in.
struct structToOutput {
	void operator() (int i) {
		cout << "Struct to output : " << i << "\n";
	}
} structToOutputObject;
 
int main(int argc, char* argv[])
{
	// lets load up some dummy data.
	vector<int> v;
	for (int i =0; i< 10; i++)
		v.push_back(i);
 
	// run through the vector using a standard function with parameter
	for_each(v.begin(), v.end(), printNumber);
	// output using a operator() method
	for_each(v.begin(), v.end(), structToOutputObject);
	return 0;
}

with the output being

Print the number from a function : 0
Print the number from a function : 1
Print the number from a function : 2
Print the number from a function : 3
Print the number from a function : 4
Print the number from a function : 5
Print the number from a function : 6
Print the number from a function : 7
Print the number from a function : 8
Print the number from a function : 9
Struct to output : 0
Struct to output : 1
Struct to output : 2
Struct to output : 3
Struct to output : 4
Struct to output : 5
Struct to output : 6
Struct to output : 7
Struct to output : 8
Struct to output : 9

How to compile with g++

g++ <filename> -o <outfilename> -std=c++11

Just a small thing encase anyone else finds this interesting as such.. but you cannot add a set of ” ” strings together in c++ without declaring one being a string.. for example

cout << "hi" + "bye" << endl;

the error would be

error: invalid operands of types 

	

When you are coding with pointers in c++ and you want to access the function/variable from that pointer deferenced, how come you cannot use something like below.

struct typeT{
   int value1;
};
 
typeT* tt = new typeT;
*tt.value1;

it is because the access element of the variable tt is higher in the compiler and thus it tries to equate

tt.value1

first, which is not a good thing because the tt has not been de-referenced and thus it is just a memory address pointer to the actual object. so you need to do

(*tt).value1

because like in maths the () will be equated first and then the access element part “.” and thus to make it easier

tt->value1

will change to

(*tt).value1

within the compiler.