File content as of revision 0:80e5f4679474:

#include "mbed.h"
#include <ctype.h>

DigitalOut kolona[4] = {dp6, dp28, dp1, dp2};
DigitalIn red[4] = {dp9, dp10, dp11, dp13};

Serial pc(USBTX, USBRX); // tx, rx
Ticker t;
int preset()
{
    for(int i=0; i<4; i++)
    {
        kolona[i] = 1;
        for(int j=0; j<4; j++)
        {
            if(red[j]==1)
            {
            kolona[i] = 0;
            return 4*i+j;
            }
        }
        kolona[i] = 0;
    }
    return -1;
}

void ispisi()
{
    switch(preset()){
    case 0:
    pc.putc('1'); break;
    case 1: 
    pc.putc('2'); break;
    case 2: 
    pc.putc('3'); break;
    case 3: 
    pc.putc('A'); break;
    case 4: 
    pc.putc('4'); break;
    case 5: 
    pc.putc('5'); break;
    case 6: 
    pc.putc('6'); break;
    case 7: 
    pc.putc('B'); break;
    case 8: 
    pc.putc('7'); break;
    case 9: 
    pc.putc('8'); break;
    case 10: 
    pc.putc('9'); break;
    case 11: 
    pc.putc('C'); break;
    case 12: 
    pc.putc('\n'); break;
    case 13: 
    pc.putc('0'); break;
    case 14: 
    pc.putc('#'); break;
    case 15: 
    pc.putc('D'); break;
    default: break;
}
}

int main() {

        t.attach(ispisi, 0.2);   
    while(1);
}