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Loops

RazaRaza Posts: 53Member
[b][red]This message was edited by Raza at 2004-11-17 1:15:13[/red][/b][hr]
Hi :-)

I am a Perl newbie.I use SiePerl 5.8.0. I wrote the following program
to output all the alphabets from a to z separated by a tab-line.
I am bewildered by the output !!!.

[code]

for($letter = 'a';$letter le 'z';$letter++)
{
print "$letter ";

}

[/code]
I expect the program to terminate after z has been printed.
However , the o/p is (Dont worry about the indentation. I directly pasted it from notepad :)) :

a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex ey ez fa fb fc fd fe ff fg fh fi fj fk fl fm fn fo fp fq fr fs ft fu fv fw fx fy fz ga gb gc gd ge gf gg gh gi gj gk gl gm gn go gp gq gr gs gt gu gv gw gx gy gz ha hb hc hd he hf hg hh hi hj hk hl hm hn ho hp hq hr hs ht hu hv hw hx hy hz ia ib ic id ie if ig ih ii ij ik il im in io ip iq ir is it iu iv iw ix iy iz ja jb jc jd je jf jg jh ji jj jk jl jm jn jo jp jq jr js jt ju jv jw jx jy jz ka kb kc kd ke kf kg kh ki kj kk kl km kn ko kp kq kr ks kt ku kv kw kx ky kz la lb lc ld le lf lg lh li lj lk ll lm ln lo lp lq lr ls lt lu lv lw lx ly lz ma mb mc md me mf mg mh mi mj mk ml mm mn mo mp mq mr ms mt mu mv mw mx my mz na nb nc nd ne nf ng nh ni nj nk nl nm nn no np nq nr ns nt nu nv nw nx ny nz oa ob oc od oe of og oh oi oj ok ol om on oo op oq or os ot ou ov ow ox oy oz pa pb pc pd pe pf pg ph pi pj pk pl pm pn po pp pq pr ps pt pu pv pw px py pz qa qb qc qd qe qf qg qh qi qj qk ql qm qn qo qp qq qr qs qt qu qv qw qx qy qz ra rb rc rd re rf rg rh ri rj rk rl rm rn ro rp rq rr rs rt ru rv rw rx ry rz sa sb sc sd se sf sg sh si sj sk sl sm sn so sp sq sr ss st su sv sw sx sy sz ta tb tc td te tf tg th ti tj tk tl tm tn to tp tq tr ts tt tu tv tw tx ty tz ua ub uc ud ue uf ug uh ui uj uk ul um un uo up uq ur us ut uu uv uw ux uy uz va vb vc vd ve vf vg vh vi vj vk vl vm vn vo vp vq vr vs vt vu vv vw vx vy vz wa wb wc wd we wf wg wh wi wj wk wl wm wn wo wp wq wr ws wt wu wv ww wx wy wz xa xb xc xd xe xf xg xh xi xj xk xl xm xn xo xp xq xr xs xt xu xv xw xx xy xz ya yb yc yd ye yf yg yh yi yj yk yl ym yn yo yp yq yr ys yt yu yv yw yx yy yz

However,when I modify the program as given below I get the expected
o/p.

[code]

for($letter = 'a';$letter le 'z';$letter++)
{
print "$letter ";

if($letter eq 'z')
{
exit ;
}
}

[/code]
The o/p now is :
a b c d e f g h i j k l m n o p q r s t u v w x y z

I dont have to do the above modification if I write the same program in another language like C for example.

Plz explain :-)



Comments

  • JonathanJonathan Posts: 2,914Member
    : I am a Perl newbie.I use SiePerl 5.8.0. I wrote the following program
    : to output all the alphabets from a to z separated by a tab-line.
    : I am bewildered by the output !!!.
    :
    : [code]
    :
    : for($letter = 'a';$letter le 'z';$letter++)
    : {
    : print "$letter ";
    :
    : }
    :
    : [/code]
    : I expect the program to terminate after z has been printed.
    : However , the o/p is (Dont worry about the indentation. I directly pasted it from notepad :)) :
    :
    : a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db dc dd de df dg dh di dj dk dl dm dn do dp dq dr ds dt du dv dw dx dy dz ea eb ec ed ee ef eg eh ei ej ek el em en eo ep eq er es et eu ev ew ex ey ez fa fb fc fd fe ff fg fh fi fj fk fl fm fn fo fp fq fr fs ft fu fv fw fx fy fz ga gb gc gd ge gf gg gh gi gj gk gl gm gn go gp gq gr gs gt gu gv gw gx gy gz ha hb hc hd he hf hg hh hi hj hk hl hm hn ho hp hq hr hs ht hu hv hw hx hy hz ia ib ic id ie if ig ih ii ij ik il im in io ip iq ir is it iu iv iw ix iy iz ja jb jc jd je jf jg jh ji jj jk jl jm jn jo jp jq jr js jt ju jv jw jx jy jz ka kb kc kd ke kf kg kh ki kj kk kl km kn ko kp kq kr ks kt ku kv kw kx ky kz la lb lc ld le lf lg lh li lj lk ll lm ln lo lp lq lr ls lt lu lv lw lx ly lz ma mb mc md me mf mg mh mi mj mk ml mm mn mo mp mq mr ms mt mu mv mw mx my mz na nb nc nd ne nf ng nh ni nj nk nl nm nn no np nq nr ns nt nu nv nw nx ny nz oa ob oc od oe of og oh oi oj ok ol om on oo op oq or os ot ou ov ow ox oy oz pa pb pc pd pe pf pg ph pi pj pk pl pm pn po pp pq pr ps pt pu pv pw px py pz qa qb qc qd qe qf qg qh qi qj qk ql qm qn qo qp qq qr qs qt qu qv qw qx qy qz ra rb rc rd re rf rg rh ri rj rk rl rm rn ro rp rq rr rs rt ru rv rw rx ry rz sa sb sc sd se sf sg sh si sj sk sl sm sn so sp sq sr ss st su sv sw sx sy sz ta tb tc td te tf tg th ti tj tk tl tm tn to tp tq tr ts tt tu tv tw tx ty tz ua ub uc ud ue uf ug uh ui uj uk ul um un uo up uq ur us ut uu uv uw ux uy uz va vb vc vd ve vf vg vh vi vj vk vl vm vn vo vp vq vr vs vt vu vv vw vx vy vz wa wb wc wd we wf wg wh wi wj wk wl wm wn wo wp wq wr ws wt wu wv ww wx wy wz xa xb xc xd xe xf xg xh xi xj xk xl xm xn xo xp xq xr xs xt xu xv xw xx xy xz ya yb yc yd ye yf yg yh yi yj yk yl ym yn yo yp yq yr ys yt yu yv yw yx yy yz
    :
    : However,when I modify the program as given below I get the expected
    : o/p.
    :
    : [code]
    :
    : for($letter = 'a';$letter le 'z';$letter++)
    : {
    : print "$letter ";
    :
    : if($letter eq 'z')
    : {
    : exit ;
    : }
    : }
    :
    : [/code]
    : The o/p now is :
    : a b c d e f g h i j k l m n o p q r s t u v w x y z
    :
    : I dont have to do the above modification if I write the same program in another language like C for example.
    :
    : Plz explain :-)
    :
    Hmmm... Your condition is that $letter is less than or equal to 'z'. So when you reach z, the condition matches and it does $letter++, which (magically) gives you aa. At this point, it gets fun because you're comparing two strings of different lengths. Clearly, the first a is less than or equal to a z, so it says "OK". It's not until it reaches the first character being a z and the second being something else that it bails out.

    A far nicer way to write this is:-

    [code]for $letter (a..z) {
    print "$letter ";
    }[/code]

    Or, if you want to be breif, even just:-

    print "$_ " for a..z;

    Or

    print join(" ", a..z);

    There's more than one way to do it. ;-)

    Jonathan


    ###
    for(74,117,115,116){$::a.=chr};(($_.='qwertyui')&&
    (tr/yuiqwert/her anot/))for($::b);for($::c){$_.=$^X;
    /(p.{2}l)/;$_=$1}$::b=~/(..)$/;print("$::a$::b $::c hack$1.");

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