C.4 Chapter 5

C.4.1 Exercise 1:

function html_img($url, $alt = '', $height = 0, $width = 0) {
    print '<img src="' . $url . '"';
    if (strlen($alt)) {
        print ' alt="' . $alt . '"';
    }
    if ($height) {
        print ' height="' . $height . '"';
    }
    if ($width) {
        print ' width="' . $width . '"';
    }
    print '>';
}

C.4.2 Exercise 2:

function html_img2($file, $alt = '', $height = 0, $width = 0) {
    print '<img src="' . $GLOBALS['image_path'] . $file . '"';
    if (strlen($alt)) {
        print ' alt="' . $alt . '"';
    }
    if ($height) {
        print ' height="' . $height . '"';
    }
    if ($width) {
        print ' width="' . $width . '"';
    }
    print '>';
}

C.4.3 Exercise 3:

I can afford a tip of 11% (30)
I can afford a tip of 12% (30.25)
I can afford a tip of 13% (30.5)
I can afford a tip of 14% (30.75)

C.4.4 Exercise 4:

Using sprintf( ) is necessary to ensure that one-digit hex numbers (like 0) get padded with a leading 0.

function build_color($red, $green, $blue) {
    $redhex   = dechex($red);
    $greenhex = dechex($green);
    $bluehex  = dechex($blue);
    return sprintf('#%02s%02s%02s', $redhex, $greenhex, $bluehex);
}

You can also rely on sprintf( )'s built-in hex-to-decimal conversion with the %x format character:

function build_color($red, $green, $blue) {
    return sprintf('#%02x%02x%02x', $red, $green, $blue);
}