Convert if statements to for loop?

Question

I've written a function in mikroC that scan the pressed key in a 4x4 keypad

void scan_key()
{
    PORTB = 0B11111110;
    if ( PORTB == 0b11101110){
        Row = 1;
        Column = 1;
        return;
    }
    if ( PORTB == 0b11011110){
        Row = 2;
        Column = 1;
        return;
    }
    if ( PORTB == 0b10111110){
        Row = 3;
        Column = 1;
        return;
    }
    if ( PORTB == 0b01111110){
        Row = 4;
        Column = 1;
        return;
    }

    PORTB = 0B11111101;
    if ( PORTB == 0b11101101){
        Row = 1;
        Column = 2;
        return;
    }
    if ( PORTB == 0b11011101){
        Row = 2;
        Column = 2;
        return;
    }
    if ( PORTB == 0b10111101){
        Row = 3;
        Column = 2;
        return;
    }
    if ( PORTB == 0b01111101){
        Row = 4;
        Column = 2;
        return;
    }

    PORTB = 0B11111011;
    if ( PORTB == 0b11101011){
        Row = 1;
        Column = 3;
        return;
    }
    if ( PORTB == 0b11011011){
        Row = 2;
        Column = 3;
        return;
    }
    if ( PORTB == 0b10111011){
        Row = 3;
        Column = 3;
        return;
    }
    if ( PORTB == 0b01111011){
        Row = 4;
        Column = 3;
        return;
    }

    PORTB = 0B11110111;
    if ( PORTB == 0b11100111){
        Row = 1;
        Column = 4;
        return;
    }
    if ( PORTB == 0b11010111){
        Row = 2;
        Column = 4;
        return;
    }
    if ( PORTB == 0b10110111){
        Row = 3;
        Column = 4;
        return;
    }
    if ( PORTB == 0b01110111){
        Row = 4;
        Column = 4;
        return;
    }

    PORTB = 0B11110000;
}

Is there a way to convert this algorithm into a loop?

Your code appears to make no sense. You are setting the value of `PORTB`, and then checking to see if the value of `PORTB` is in some *other* set of values. What is going on here? — Oliver Charlesworth, May 01 '11 at 22:15
Actually, I'm using an interrupt (PORTB interrupt) and this code what I got after many tries. Now, I'm interested in converting this code to a loop — Eng.Fouad, May 01 '11 at 22:19

Chris Cooper · Accepted Answer · 2011-05-01T23:23:36.743

5

Yes. (At least assuming you don't actually mean to have those assignments before each block of ifs. I assume they were there for testing? otherwise your code doesn't make sense.)

At the very least, you can put each of the binary values into an array, and construct a loop like this:

int portValue[4][4] = {{0b11101110, 0b11011110, 0b10111110, 0b01111110}, {//...Rest of values here }}

int loop_col = 0;
int loop_row = 0;

for (loop_col = 0; loop_col < 4; loop_col++){
    for (loop_row = 0; loop_row < 4; loop_row++){
         if ( PORTB == portValue[loop_col][loop_row]){
             Row = loop_row + 1;
             Column = loop_col + 1;
             return;
         }
    }
}

edited May 01 '11 at 23:23

answered May 01 '11 at 22:18

Chris Cooper

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+1 for elegant solution. – Athabaska Dick May 01 '11 at 22:20
2

+1: But the array indices are wrong (need to subtract 1 before indexing). – Oliver Charlesworth May 01 '11 at 22:35
Actually, I think I understand the OP's code now (well, sort of). On a PIC, ports are not only bidirectional, but also have all sorts of magical peripherals on them. I think the setting of the register before reading is to set up some kind of interrupt. So it may well be needed. – Oliver Charlesworth May 01 '11 at 22:38
@Oli: Ah yes, thank you. Also, interesting about the PIC ports. Makes for logically confusing code though. – Chris Cooper May 02 '11 at 00:08

score 1 · Answer 2 · edited May 01 '11 at 22:27

Yes of course.

First do some array with your values. we'll call it t[] and second is d[][] // two dimensional array

and lets do double loop

for(i=1;i<=4;i++)
{
    cur_value=t[i]; // our value

    for(j=1;j<=4;j++)
    {
        right_side_value=d[i][j];
        if(cur_value==right_side_value)
        {
            rows=i;
            columns=j;
            return;
        }
    }
}

Hope that helps.

Don't know if 1 dimensional array is only needed for d values, didnt check every number

Convert if statements to for loop?

2 Answers2