how to plot 3 graphs with (+) sign convention?

Hello... I am an mechanical engineering student learning MATLAB... I would like to know how can i graph 3 functions all done completely. I mean, when first graph meets condition of lower than 0, all the loops broken and other two graphs lies upper side of 0. I want all 3 graphs meet 0, and plot them on the figure... Help needed....T_T

% set random position of me and computer my_position = 50 * rand(1); com_position = 50 + 50 * rand(1);

% show where computer and i am plot(my_position, 0, 'go');hold on; plot(com_position, 0, 'mo');hold on;

% 10 chances to shoot for i = 1:10 % get speed and angle with my input cannon_angle = input('Input angle:'); cannon_speed = input('Input speed:');

    % set 3 speeds, one with 2 degree up and another with 2 degree down
    x_vel = cannon_speed * cosd(cannon_angle);
    y_vel = cannon_speed * sind(cannon_angle);

    x1_vel = cannon_speed * cosd(cannon_angle+2);
    y1_vel = cannon_speed * sind(cannon_angle+2);

    x2_vel = cannon_speed * cosd(cannon_angle-2);
    y2_vel = cannon_speed * sind(cannon_angle-2);

    t=0;

    while (1)
%       Vx = Vox;
%       Vy = Voy - 9.81*t;
%       Sx = Vox*t;
%       Sy = Voy*t - 0.5*9.81*t^2
        x_pos = my_position + x_vel * t;
        y_pos = y_vel * t - 0.5*9.81*(t^2);
        plot(x_pos, y_pos, 'ro'); hold on;
        pause(0.01);
        t = t + 0.01;
        if y_pos<0
            break;
        end
        x1_pos = my_position + x1_vel * t;
        y1_pos = y1_vel * t - 0.5*9.81*(t^2);
        plot(x1_pos, y1_pos, 'ks'); hold on;
        pause(0.01);
        t = t + 0.01;
        if y1_pos<0
            break;
        end
        x2_pos = my_position + x2_vel * t;
        y2_pos = y2_vel * t - 0.5*9.81*(t^2);
        plot(x2_pos, y2_pos, 'bd'); hold on;
        pause(0.01);
        t = t + 0.01;
        if y2_pos<0;
            break;
        end

    end

    if abs(x1_pos - com_position) <3
        sprintf('YOU GOT ME')
       break;
    elseif abs(x2_pos - com_position) <3
        sprintf('YOU GOT ME')
       break;
    elseif abs(x_pos - com_position) <3
        sprintf('YOU GOT ME')
       break;
    end
end

if i==10 disp('YOU FAILED'); end