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[Powered by Google Translate] Precendence ni jinsi sisi kujibu swali, nini tunapaswa kufanya operesheni ya kwanza?

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Kama kutatua equations math au mistari parsing wa code kompyuta,

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kuna sheria kali ya precedence ambayo sisi kuambatana

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ili wote kompyuta na watu wanaweza kupata matokeo sawa.

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>> Kwanza mbali, utawala muhimu kukumbuka, hasa katika kupima mdudu,

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ni kwamba sisi daima kazi kutoka mabano ndani nje.

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Kutumia mabano ziada inaweza kusaidia debugging mbinu,

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lakini siyo vizuri mazoezi ya takataka code yako kwa mabano unneeded.

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Kuchukua muda kujifunza msingi operator sheria ya kuendelezwa.

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>> pili kanuni ya jumla ni kwamba wakati waendeshaji kuwa priorty sawa,

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wewe tu kutatua kutoka kushoto kwenda kulia.

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Wakati wa kushughulika na math rahisi sisi kuanza na mabano,

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kisha kufanya kuzidisha na kugawanya, na mwishowe kufanya kujumlisha na kutoa.

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Kuzidisha na kugawanya kuwa na kipaumbele huo,

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kwa sababu wao ni kimsingi kufanya operesheni moja.

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Baada ya mgawanyiko wote ni tu kuzidisha na Inverse ya thamani.

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Vile vile, utoaji ni tu kuongeza thamani hasi.

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>> Hebu kufanya mfano.

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Kufuatia amri ya precedence, tutaweza kuanza na mabano. Tisa minus 1.

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Hiyo itatupa 8. Kisha tunaweza kuendelea na mgawanyiko na kuzidisha.

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Tutaweza kutatua kutoka kushoto kwenda kulia. Hivyo 10 kugawanywa na 2 ni 5.

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Tuna mara 5 8 hapa, na kwamba atatupa 40.

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Kisha sisi kuendelea na utaratibu ijayo ya kuendelezwa.

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Hivyo sisi ni wa kushoto na 3 plus minus 40 1.

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Tena tu kutatua kushoto na kulia,

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sababu kuna sawa kipaumbele kati ya kujumlisha na kutoa.

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Tunaweza kusema 3 plus 40 ni 43, minus 1 ni 42. Hiyo ni jibu letu.

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>> Kuna aina 2 ya kampuni za pungufu na increment;

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fomu kiambishi awali, na fomu suffix.

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fomu suffix, i + +, ni kawaida kutumika katika kwa tanzi,

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ambayo ina maana kwamba thamani ya sasa ni kutumika katika kujieleza, na kisha ni incremented.

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Hivyo thamani itakuwa tu tofauti wakati ujao variable ni kutumika.

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Kwa upande mwingine, increment kiambishi awali au pungufu ina maana kwamba thamani ya sasa ya

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ni incremented au decremented kwanza, na kisha ni kutumika katika kujieleza.

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>> Hebu chukua mfano kwa x integer.

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Tutaweza kuliweka sawa na 5.

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Kama sisi kutumia operator suffix juu yake na kusema x + +, x juu ya mstari huu ni bado 5.

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Kama tulikuwa na magazeti ni nje tunataka kupata thamani 5.

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Lakini kwenda mbele x1 ukweli sawa na 6.

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Hivyo haki hapa kwenye x line hii ni sawa na 6, na kama sisi kuchapishwa nje tunataka kupata thamani 6.

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Sasa kama sisi kutumika operator kiambishi awali, + + x, x ni incremented kwanza, na kisha thamani ni kutumika.

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Hivyo ni sawa na 7 juu ya mstari huu.

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Incrementing bila shaka 6-7, na kama tulikuwa na magazeti ni nje tunataka kupata thamani 7.

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>> nuance mwisho katika precendence kwamba tutaangalia mikataba na nukuu pointer.

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operator dereference, nyota, ina kipaumbele juu ya waendeshaji msingi math,

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lakini si zaidi ya incement suffix na waendeshaji pungufu.

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Hii imesababisha sisi mfano wetu wa mwisho.

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Hebu x integer na kuliweka sawa na 7.

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Tutaweza pia kufanya y pointer na kuliweka sawa na anuani ya x.

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Hivyo kwamba wakati sisi dereference y tunapaswa kupata thamani 7.

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Sasa katika mstari wa kanuni, tuna hali fulani utata.

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Je, sisi dereferencing y kwanza, na kisha incrementing thamani 7?

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Au ni sisi incrementing pointer na kisha dereferencing yake?

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Kwa kweli, kwa sababu increment suffix operator ina precedence juu ya

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operator dereference, sisi ni kujaribu increment y pointer,

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ambayo itakuwa hoja pointer na ukubwa wa ka int.

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Kimsingi, akitupa anwani katika baadhi ya uhakika tofauti kabisa katika kumbukumbu,

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na kisha sisi ni dereferencing yake.

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Hivyo hii ni sana maana mstari.

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Kama sisi kweli alitaka increment thamani ya 7,

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sisi ingekuwa kuweka operator dereference na y katika mabano.

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Kisha tunaweza increment yake.

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Hivyo wakati sisi isingekuwa incrementing x thamani na ya pili mstari wa mwisho wa code,

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katika mstari wa mwisho wa code tunataka infact dereference y

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kupata x thamani na increment kwamba.

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Tutakuwa kushoto na thamani sawa na x 8.

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>> Hapa ni recap ya haraka ya sheria precendence kwamba tumekuwa kuzungumzwa.

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Tutaweza kuanza na mabano ndani na kazi nje.

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Kisha sisi hoja juu ya suffix operators kama i + + au i -.

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Kisha dereference na anuani ya kampuni kama nyota x au ampersand x,

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na waendeshaji kiambishi awali kama + + i au - i.

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Hatimaye sisi kufanya shughuli rahisi math kama mgawanyiko kuzidisha,, modulo.

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Kisha Aidha, kutoa.

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Hiyo precendence. Mimi nina Jordan Jozwiak, na hii ni CS50.

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Tutaweza dereference na kutumia anwani na - jinsi ya kufanya wewe maneno ya kwamba?

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Mimi nina kufanyika. Sawa.