1
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>> [Daqq tal-mużika]

2
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>> ZAMYLA Chan: Ejja tindirizza jirkupraw.

3
00:00:11,150 --> 00:00:14,030
Jirkupraw huwa probabbilment PSET favorit tiegħi,
u prinċipalment għaliex naħseb li huwa

4
00:00:14,030 --> 00:00:15,650
tassew, tassew jibred.

5
00:00:15,650 --> 00:00:19,040
Bażikament, int tingħata memorja
fajl card li fih

6
00:00:19,040 --> 00:00:20,900
stampi ġew imħassra.

7
00:00:20,900 --> 00:00:23,650
Imma dak li int ser
tagħmel huwa jirkupraw lilhom kollha.

8
00:00:23,650 --> 00:00:24,250
>> OK.

9
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Allura huwa verament eċċitanti, imma forsi
ftit intimidanti, għax int

10
00:00:28,230 --> 00:00:32,430
mogħtija fajl C vojta u
inti għandek timla pulzieri

11
00:00:32,430 --> 00:00:36,250
OK, so ejja jiksru dan
f'partijiet maniġġabbli.

12
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Int ser ikollok tixtieq li tiftaħ il-
fajl karta tal-memorja.

13
00:00:38,160 --> 00:00:39,900
Dan jidher sempliċi biżżejjed.

14
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Imbagħad, issib il-bidu
ta 'immaġni JPG.

15
00:00:43,030 --> 00:00:46,740
Il-fajls kollha dwar dan il-memorja
karta ser ikunu jpgs.

16
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Imbagħad, ladarba inti ssib il-bidu,
int ser tiftaħ JPG ġdida, li

17
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huwa, bħal, joħolqu JPG, u jiktbu 512
byte fi żmien sakemm JPG ġdida hija

18
00:00:57,610 --> 00:01:02,930
misjuba, u jispiċċa l-programm, ladarba
inti tiskopri l-aħħar tal-fajl.

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>> Allura l-ewwel passi ewwel huwa li tiftaħ
il-fajl karta tal-memorja.

20
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Imma inti taf dan diġà, u hemm
fajl funzjoni I / O li għaddej biex

21
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jkunu utli ħafna.

22
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OK.

23
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Allura x'inhuma jpgs?

24
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Għaliex għandna bżonn għall-bidu dan.

25
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Well, jpgs, bħad mapep bit,
huma biss sekwenzi ta 'bytes.

26
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Fortunatament, kull JPG jibda ma 'jew
0xff, 0xd8, 0xff, 0xe0, sekwenza waħda

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ta 'bytes, jew ieħor
sekwenza ta 'bytes.

28
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>> Allura dawn l-erba 'bytes jindikaw
il-bidu ta 'JPG.

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Xejn għajr dawk iż-żewġ kombinazzjonijiet
ta 'erba' bytes.

30
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U fortunatament għalina, ieħor fatt li aħna
jistgħu jieħdu vantaġġ minnu huwa li kull

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JPG huwa maħżun ġenb ma 'ġenb
fuq il-karta tal-memorja.

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Stajt rappreżentati l-istruttura ta '
karta tal-memorja skematikament fuq dan

33
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slide hawnhekk.

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Hawnhekk, kull kwadru, kull rettangolu,
jirrappreżenta 512 bytes, u jibda

35
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ma 'griż li aħna ma
verament ikollhom JPG.

36
00:02:01,750 --> 00:02:05,700
>> Imma allura aħna finalment hit
blokk bi stilla.

37
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Dan ifisser li l-ewwel erba 'bytes barra
ta 'dawk 512 wieħed minn dawk iż-żewġ

38
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jibdew sekwenzi ta 'JPG.

39
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U aħna jmorru minn hemm, u mbagħad darba
JPG wieħed jispiċċa, jibda dak li jmiss.

40
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Aħna qatt ma jkollhom kwalunkwe aktar
ispazju griż fil-bejn.

41
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>> Imma kif nistgħu fil-fatt taqra dan, u
aqra l-512 bytes sabiex inkunu jistgħu jagħmlu

42
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il-paragun l-ewwel post?

43
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Well, ejja mur lura għall fread, li
jieħu fil-Struct li se jkun fiha

44
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l-bytes li int qari.

45
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Allura int ser tpoġġi
dawk fil hemm -

46
00:02:36,570 --> 00:02:42,192
id-daqs, in-numru, u mbagħad inpointer
li inti qed taqra minn.

47
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Issa, irridu li jaqra 512 fi żmien, u
irridu li jaħżen dan fil-buffer,

48
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Jien ser sejħa tiegħu.

49
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>> Bażikament, aħna qed tmur biex iżommu
fuq dawk il-512 bytes u ma

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affarijiet magħha, right?

51
00:02:55,500 --> 00:02:58,260
Aħna qed kemm ser iqabblu l-ewwel
erba 'bytes, jew aħna qed tmur biex

52
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taqraha fi, OK?

53
00:02:59,830 --> 00:03:05,050
Mela allura l-pointer data se mbagħad
jservi bħala buffer tiegħek, u l-

54
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inpointer, ukoll, li jinsab biss jmorru
li tkun karta tal-memorja tiegħek.

55
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>> Lura għall skematika tagħna karta tal-memorja.

56
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Aħna qed tmur biex taqra 512 bytes fi żmien,
ħażna kull blokk 512-byte

57
00:03:14,690 --> 00:03:19,190
ġo buffer, azjenda fuq dawk
buffer, dawk 512 bytes, sakemm nafu

58
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eżattament x'għandhom jagħmlu magħhom.

59
00:03:22,000 --> 00:03:25,960
Allura l-bidu ma jkunx xejn, hekk
aħna ser taqra l-buffer, din titqabbel, u

60
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aħna mhux se bżonn li tagħmel xejn magħha.

61
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U mbagħad, aħna finalment hit stilla
blokk, li jfisser li konna

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misjuba ewwel JPG tagħna.

63
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Allura l-buffer issa għandhom
bytes minn dak JPG.

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>> Il-ħin li jmiss 512 bytes, għaliex qed
ma blokk stilla, huma wkoll

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parti minn dik JPG.

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U jpgs huma kontinwi minn hemm
fuq in, sakemm aħna laqat il JPG jmiss.

67
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U allura l-buffer mbagħad istivi
512 bytes għal dak JPG, u

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bqija, u ibqa 'sejjer hekk.

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OK.

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00:03:54,250 --> 00:03:58,980
>> Allura ladarba inti hit l-ewwel starred
blokk, l-ewwel JPG, kif taħseb li

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attwalment, ukoll, tiftaħ it?

72
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Ejja jagħmlu JPG ġdid.

73
00:04:04,990 --> 00:04:08,846
Il filenames għal JPG ser
tkun fil-format, numru, numru,

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number.jpg, b'mod li dawn qed jismu fl
l-ordni li fih ikunu jinstabu,

75
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jibdew minn 0.

76
00:04:14,780 --> 00:04:19,890
>> Allura l-ewwel JPG li inti
ssib ser jiġu 000.jpg.

77
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Allura, probabbilment idea tajba li jżomm track
ta 'kemm jpgs inti stajt sabet s'issa.

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Allura dak hu l-isem ta 'fajl.

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Imma kif inti fil-fatt tagħmel dan?

80
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Well, aħna qed tmur biex tuża
funzjoni msejħa sprintf.

81
00:04:34,310 --> 00:04:38,260
A ftit simili għal printf, fejn
inti tista 'tuża placeholders għal kordi,

82
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ħlief fil-każ preżenti, sprintf se print
il-fajl out għal ġol-kurrent

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direttorju, mhux fil-terminal.

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>> OK.

85
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Allura hawn naraw li għandna titolu,
firxa char li ser taħżen l-

86
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string riżultanti, u aħna jgħaddu fil-
titolu tas-sekwenza attwali bil-

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placeholder, bħad konna
tgħallmu li tagħmel ma printf.

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Iżda dan il-kodiċi li għandi hawn
se tagħti 2.jpg, mhux 002.jpg.

89
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So I ser tħalli lilek biex issir taf kif
timmodifika l-placeholder li jagħmlu l-

90
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isem korrett.

91
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>> OK.

92
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Allura ladarba inti stajt sprintf'd allura inti tista '
tiftaħ dan il-fajl, minħabba li teżisti

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direttorju tiegħek, ma fopen, bl-użu
titolu, u mbagħad kull sura trid

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li tiftaħ dan il-fajl pulzieri

95
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Allura issa li aħna ħadthom fetħet fajl JPG ġdid,
issa nistgħu jikteb 512 bytes fi

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00:05:30,260 --> 00:05:33,320
time, sakemm tinstab JPG ġdid.

97
00:05:33,320 --> 00:05:36,640
Mela ejja tagħti ħarsa ieħor
fil-sintassi ta fwrite.

98
00:05:36,640 --> 00:05:40,060
>> Naf li jien turi dan slide a
ħafna, iżda I biss jixtiequ jagħmlu ċert li

99
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inti guys ma jsibux wisq konfuż, għaliex
Naf li huwa faċli ħafna li

100
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ħallat l-ewwel u l-aħħar
argument, b'mod partikolari.

101
00:05:47,000 --> 00:05:54,390
Imma ftakar li int bil-miktub mill-
buffer fil-immaġini fajl out tiegħek.

102
00:05:54,390 --> 00:05:59,250
>> Issa li taf kif il-write 512
bytes fil-fajl JPG tiegħek li inti ħadthom

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maħluqa, ukoll, aħna tixtieq li twaqqaf dik
proċess ladarba aħna ħadthom laħqu t-tmiem ta '

104
00:06:03,230 --> 00:06:06,720
karta tagħna, għax mhux se jkun hemm
xi ritratti aktar biex jinstabu.

105
00:06:06,720 --> 00:06:10,760
Mela ejja mmorru lura għall fread
darba aktar, I wegħda.

106
00:06:10,760 --> 00:06:15,600
fread prospetti kif ħafna oġġetti ta 'daqs,
daqs, kienu lesti fl b'suċċess.

107
00:06:15,600 --> 00:06:19,440
Idealment, dan se jkun x'ikun
inti tgħaddi fl għal numru, id-dritt?

108
00:06:19,440 --> 00:06:24,140
Għax int tipprova taqra numru
ta 'elementi ta' daqs, id-daqs.

109
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Imma jekk fread mhux kapaċi taqra li
numru ta 'elementi, allura dan ser jirritorna

110
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kwalunkwe numru jinqara b'suċċess.

111
00:06:32,530 --> 00:06:36,310
>> Issa, ħaġa waħda importanti li wieħed jinnota huwa
li jekk tuża fajl ieħor I / O

112
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funzjoni bħal fgetc, dan ser jerġa 'lura wkoll
oġġetti kemm jinqara b'suċċess.

113
00:06:43,860 --> 00:06:48,000
X'hemm utli dwar din il-funzjoni huwa
li jekk inti tuża l-funzjonijiet ġewwa ta '

114
00:06:48,000 --> 00:06:53,190
kundizzjoni, dan ser tesegwixxi innifsu waqt
tiddetermina dik il-kundizzjoni, li hija

115
00:06:53,190 --> 00:06:54,340
biss verament utli.

116
00:06:54,340 --> 00:07:00,440
Mela jekk għandek dan kondizzjonijiet, ngħidu aħna,
jekk buffer fread, DOG sizeof, 2,

117
00:07:00,440 --> 00:07:04,870
pointer, ugwali daqs 1, li
ifisser li nixtieq li taqra

118
00:07:04,870 --> 00:07:06,540
2 klieb fil-ħin.

119
00:07:06,540 --> 00:07:13,490
Imma jekk fread prospetti 1 minflok 2 bħala
mistenni, dan ifisser li hemm 2

120
00:07:13,490 --> 00:07:16,480
klieb xellug fil-fajl tiegħi, iżda pjuttost 1.

121
00:07:16,480 --> 00:07:22,450
Iżda jekk dan jirritorna 2, imbagħad I għad għandhom
dawk 2 klieb ġewwa ta 'buffer tiegħi.

122
00:07:22,450 --> 00:07:26,280
>> Allura issa li jagħtik sens ta 'kif
jikkontrolla l-aħħar tal-fajl, iżda

123
00:07:26,280 --> 00:07:28,940
ejja jgħaddu issa l-loġika.

124
00:07:28,940 --> 00:07:32,460
Kif nistgħu attwalment biċċa kollha
ta 'dawn l-elementi flimkien?

125
00:07:32,460 --> 00:07:36,880
Ladarba aħna hit ewwel JPG tagħna, minn
nafu li jpgs huma maħżuna

126
00:07:36,880 --> 00:07:40,910
contiguously, aħna ser tkun bil-miktub sakemm
aħna jilħqu t-tmiem tal-fajl biljett.

127
00:07:40,910 --> 00:07:43,950
Iżda aħna ma jridu jiktbu
xejn sa dakinhar.

128
00:07:43,950 --> 00:07:48,710
Għalhekk huwa importanti, mhux biss li aħna qed fuq
il-bidu ta 'JPG ġdida, iżda jekk

129
00:07:48,710 --> 00:07:50,655
aħna stajt diġà sabet JPG jew le.

130
00:07:50,655 --> 00:07:55,390
>> Jekk Hu l-bidu ta 'JPG ġdid, aħna ser
tixtieq li tagħlaq tagħna fajl JPG attwali jekk

131
00:07:55,390 --> 00:07:59,110
aħna għandna waħda miftuħa, u miftuħ
waħda ġdida li tikteb fis.

132
00:07:59,110 --> 00:08:03,340
Jekk mhuwiex il-bidu tal-JPG ġdid,
għalkemm, aħna ser iżommu l-istess fajl JPG

133
00:08:03,340 --> 00:08:05,910
tiftaħ u jiktbu f'dak.

134
00:08:05,910 --> 00:08:10,100
Aħna ser jiktbu buffer tagħna fis liema
Fajl JPG għandna miftuħa, sakemm

135
00:08:10,100 --> 00:08:12,120
aħna għandna waħda miftuħa, tal-kors.

136
00:08:12,120 --> 00:08:16,190
Jekk aħna ma sabu ewwel JPG tagħna
għadhom, aħna ma jiktbu xejn.

137
00:08:16,190 --> 00:08:20,290
U dan il-proċess ikompli sakemm inti
jilħqu t-tmiem tal-fajl biljett.

138
00:08:20,290 --> 00:08:23,410
>> U fl-aħħarnett, inneħħu inti tixtieq li tagħmel
ċert li inti fclose kwalunkwe

139
00:08:23,410 --> 00:08:25,800
fajls li inti stajt fopened.

140
00:08:25,800 --> 00:08:28,360
Ladarba int komdu mal-
kunċetti, tagħti ħarsa lejn uħud

141
00:08:28,360 --> 00:08:30,840
pseudocode, li stajt inklużi hawn.

142
00:08:30,840 --> 00:08:34,830
L-ewwel, inti tixtieq li tiftaħ il-fajl biljett,
u mbagħad irrepeti l-proċess ta 'wara

143
00:08:34,830 --> 00:08:37,144
sakemm inti stajt laħqu l-
tmiem tal-biljett.

144
00:08:37,144 --> 00:08:40,880
Inti tixtieq li taqra 512 bytes
fi buffer.

145
00:08:40,880 --> 00:08:43,934
Bl-użu li buffer, tixtieq tkun taf biex jiċċekkjaw
jekk int fil-bidu ta '

146
00:08:43,934 --> 00:08:45,300
JPG ġdid jew le.

147
00:08:45,300 --> 00:08:48,400
U ir-risposta għal din id-domanda se
jaffettwawx l-amministrazzjoni fajl tiegħek -

148
00:08:48,400 --> 00:08:51,940
li fajls li inti tiftaħ, li
dawk do inti qrib.

149
00:08:51,940 --> 00:08:55,220
>> Imbagħad, usted diġa 'sabu JPG?

150
00:08:55,220 --> 00:08:57,740
Kif inti kienu ġew żamma
track ta 'li?

151
00:08:57,740 --> 00:09:01,735
Imbagħad, jiddependi fuq li, inti ser jew
jikteb fil-JPG attwali li inti

152
00:09:01,735 --> 00:09:07,090
ikollhom miftuħa, jew ma jiktbu fil-livelli kollha,
għaliex inti ma sabu JPG s'issa.

153
00:09:07,090 --> 00:09:10,870
Finalment, ladarba inti stajt laħqu t-tmiem ta '
il-fajl, tixtieq tkun taf biex jagħlqu kwalunkwe

154
00:09:10,870 --> 00:09:12,590
fajls li inti għandek miftuħa fadal.

155
00:09:12,590 --> 00:09:14,590
Irridu nkunu puliti hawn.

156
00:09:14,590 --> 00:09:18,790
>> U ma 'dan, inti stajt rkuprati kollha
il-fajls neqsin minn dak tal-memorja

157
00:09:18,790 --> 00:09:21,620
karta, li huwa proeza pretty aqwa.

158
00:09:21,620 --> 00:09:23,430
Allura pat lilek innifsek fuq id-dahar.

159
00:09:23,430 --> 00:09:27,560
Iżda, hemm wieħed element aktar
l PSET, li hija l-konkors.

160
00:09:27,560 --> 00:09:30,920
Inti ser issib li kollha ta 'l-istampi
li ħadthom rkuprati huma attwalment

161
00:09:30,920 --> 00:09:32,820
stampi ta 'staff CS50'S.

162
00:09:32,820 --> 00:09:38,500
Mela jekk int fuq il-kampus jew x'imkien
qarib, allura inti tista 'tieħu stampi ma

163
00:09:38,500 --> 00:09:42,600
il-persunal, u s-sezzjoni li għandha l-
aktar stampi ma membri tal-persunal

164
00:09:42,600 --> 00:09:46,940
mill-fajls irkuprati tagħhom se
tikseb premju tal-biża.

165
00:09:46,940 --> 00:09:50,650
Ma 'dan, allura inti ħadthom lest
l jirkupraw PSET.

166
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Jisimni Zamyla, u dan huwa CS50.

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