How do you convert binary 0001,0010,0100,1000 to 0,1,2,3 to index a 4x4 2D array?

Question

I am reading key presses from a 4x4 keypad connected to a microcontroller but since a keypad is divided into rows and columns, it only reads 0001 or 1000 etc to specify row and column.

I have a character lookup table for the keypad in my main like:

char keys[4][4]={
        //       c3  c2  c1  c0
                {'1','2','3','A'},  //row4 PortA4 1000 

                {'4','5','6','B'},  //row3 PortA3 0100

                {'7','8','9','C'},  //row2 PortA2 0010

                {'*','0','#','D'}   //row1 PortA1 0001

                };

I want the inputs read from the keypad to be able to directly index this table and print out said character, but naturally, any number above 3 is out of bounds. I want to be able to use something like

printf("Key Pressed: %c",keys[indexrow][indexcolumn]);

but right now I have it hardcoded as follows:

...

while(1)
    {
        //begin polling
        row_data=0x01;//bottom row
        bus.IOWrite(PortA,row_data);
        column_data=b&bus.IORead(PortB);
        if((column_data & b)!=0)
        {
            //printf("Keypress detected @row %0b @column %0b",row_data,column_data);
            switch(column_data)
            {
                case 0x01:printf("Key Pressed: D");break;
                case 0x02:printf("Key Pressed: #");break;
                case 0x04:printf("Key Pressed: 0");break;
                case 0x08:printf("Key Pressed: *");break;
                default: break;
            }

        }
.
.
.

I suppose it could be simpler to just create an 8x8 table with lots of empty spaces within, but that would not be as pleasing to look at.

Answer 1

You switch statement could help you derive an index into your 2-dimensional array like this:

            switch(column_data)
            {
                case 0x01:column_index=0;break;
                case 0x02:column_index=1;break;
                case 0x04:column_index=2;break;
                case 0x08:column_index=3;break;
                default: /* probably needs handling here */ break;
            }

... but, what happens when more than one button is pressed.

Answer 2

You could write a code to convert the number format

# include <stdio.h>

int main()
{
  int numberToBeConverted = 0x08;
  int i,j;
  for(i=numberToBeConverted, j=1; i!=0;i/=2,j++)
  {
    if(i&1==1)
    {
      printf("%d\n",j);
      //Whatever you want to do with the key thats pressed
    }

  }
  return 0;
}