Assembly Loop printing Stars

.model small
.stack 100h
.data
a db ?
.code
    main proc
        mov ax,@data
        mov ds,ax

        mov ah,1
        int 21h
        sub al,48
        mov a,al

        mov ah,2
        mov dl,10
        int 21h
        mov dl,13
        int 21h

        mov ch,0
        mov cl,a
        mov bl,1
        p:
        mov cx,bx
        q:
        cmp bl,a
        jg exit
        mov ah,2
        mov dl,'*'
        int 21h
        loop q

        mov ah,2
        mov dl,10
        int 21h
        mov dl,13
        int 21h
        inc bl
        loop p


        exit:
        mov ah,4ch
        int 21h
        main endp
    end main