Calculating if a point (x,y) is in between two other points on a plane

in_between.c

struct point {
    int x;
    int y;
}

void is_between(struct point the_point, struct point a, struct point b) {
    int cross_product = (the_point.y - b.y) * (a.x - b.x) - (the_point.x - b.x) * (a.y - b.y);
    
    if (abs(cross_product) != 0) {
        return false;
    }
    
    int dot_product = (the_point.x - b.x) * (a.x - b.x) + (the_point.y - b.y) * (a.y - b.y);
    if (dot_prouduct < 0) {
        return false;
    }
        
    int squaredlengthba = (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
    if (dot_product > squaredlengthba) {
        return false;
    }
    
    return true;
}

in_between_linewise.vim

function! s:check_if_cursor_in_cursors(thecursor, a, b)
    " row = 1 , column = 2

    if a:thecursor[1] ># a:a[1] && a:thecursor[1] <# a:b[1]
        return 1
    elseif a:thecursor[1] ># a:a[1] && a:thecursor[1] ==# a:b[1] &&
                \ a:thecursor[2] <=# a:b[2]
        return 1
    elseif a:thecursor[1] ==# a:a[1] && a:thecursor[2] >=# a:a[2] &&
                \ a:thecursor[1] <# a:b[1]
        return 1
    elseif a:thecursor[1] ==# a:a[1] && a:thecursor[2] >=# a:a[2] &&
                \ a:thecursor[1] ==# a:b[1] && a:thecursor[2] <=# a:b[2]
        return 1
    endif

    return 0
endfunction