{"id":1343,"date":"2011-08-26T17:50:55","date_gmt":"2011-08-26T15:50:55","guid":{"rendered":"http:\/\/www.iprog.it\/blog\/?p=1343"},"modified":"2012-04-30T18:56:46","modified_gmt":"2012-04-30T17:56:46","slug":"programmazione-ios-e-mac-costrutti-di-selezione-e-operatori-logici","status":"publish","type":"post","link":"https:\/\/www.iprog.it\/blog\/objective-c-teoria\/programmazione-ios-e-mac-costrutti-di-selezione-e-operatori-logici\/","title":{"rendered":"Programmazione iOS e Mac, Costrutti di selezione e operatori logici"},"content":{"rendered":"

\"\"<\/a><\/p>\n

Un costrutto di selezione denota la scelta (selezione) tra due insiemi di istruzioni, in dipendenza del valore di una condizione (predicato) .<\/p>\n

Un costrutto di selezione deve specificare<\/p>\n

1)Una condizione che pu\u00f2 assumere due valori vero o falso<\/p>\n

2)Due insiemi di istruzioni<\/p>\n

Costrutto di selezione IF<\/span><\/p>\n

\"\"<\/a><\/p>\n

Operatori Logici<\/span><\/p>\n

\"\"<\/a><\/p>\n

Operatori Logici e di eguaglianza<\/span><\/p>\n

== —————-> uguale<\/p>\n

!= \u00a0—————-> diverso<\/p>\n

Hanno priorit\u00e0 inferiore \u00a0a quella degli operatori di relazione<\/p>\n

Operatori logici di connessione<\/span><\/p>\n

! ————->negazione (not)<\/p>\n

&& ———-> congiunzione (and)<\/p>\n

|| ————> disgiunzione (or)<\/p>\n

Hanno priorit\u00e0 inferiore a quella di tutti gli altri operatori logici<\/p>\n

Esempio: programma Objective-C per il calcolo del valore assoluto di un numero\u00a0<\/span><\/p>\n

[code lang=”objc”]&lt;\/pre&gt;
\n&lt;div&gt;
\n#include &lt;Cocoa\/Cocoa.h&gt;
\n Int main(int argc, char *argv[]) {
\n&lt;pre&gt; float x,val_assoluto;
\n NSLog(@\u201cinserire un numero \u201d);
\n scanf(\u201c%f\u201d,&amp;x);\/\/salviamo il valore della variabile immessa da input
\n if (x &gt;= 0.0)<\/p>\n

val_assoluto = x;
\n else&lt;\/pre&gt;
\nval_assoluto = -x; NSLog(@\u201c\\n valore assoluto di %f
\n&lt;pre&gt; = %f\\n\u201d,x,val_assoluto);
\n return 0;&lt;\/pre&gt;
\n}<\/p>\n

[\/code]<\/p>\n

Costrutto di selezione nidificato\u00a0<\/span><\/p>\n

\"\"<\/a><\/p>\n

Esempio: programma Objective-C per determinare se un numero intero \u00e8 positivo, nullo o negativo<\/p>\n

[code lang=”objc”]&lt;\/pre&gt;
\n&lt;div&gt;
\n#include &lt;Cocoa\/Cocoa.h&gt;
\n int main(int argc, char *argv[])<\/p>\n

{
\n int x;
\n NSLog(@\u201c inserire un numero\\n\u201d); scanf(\u201c%i\u201d,&amp;x);
\n if (x &gt; 0)
\n&lt;pre&gt; NSLog(@\u201c%i e\u201f positivo\u201d,x);
\n else if (x == 0)<\/p>\n

NSLog(@\u201c%i e\u201f nullo\u201d,x);
\n else<\/p>\n

NSLog(@\u201c%i e\u201f negativo\u201d,x);
\n return 0;&lt;\/pre&gt;
\n}&lt;\/div&gt;
\n&lt;div&gt;[\/code]<\/p>\n

Costrutti \u00a0di ripetizione<\/span><\/div>\n
While<\/span><\/div>\n
[code lang=”objc”]
\nWhile &lt;predicato&gt;
\n&lt;corpo del ciclo&gt;
\nendwhile
\n[\/code]<\/p>\n

repeat until<\/span><\/p>\n

[code lang=”objc”]
\nrepeat
\n&lt;corpo del ciclo&gt;
\nuntil &lt;predicato&gt;
\n[\/code]<\/p>\n

do while<\/span><\/p>\n

[code lang=”objc”]
\ndo{
\n&lt;corpo del ciclo&gt;
\n}
\nwhile(&lt;predicato&gt;);
\n[\/code]<\/p>\n

Il costrutto for in Obj-c \u00e8 equivalente a while<\/span><\/p>\n

[code lang=”objc”]
\nfor (i=a;i&lt;=b;i=i+c)
\n{
\n&lt;corpo del ciclo&gt;
\n}
\noppure possiamo scrivere
\ni=a
\nwhile (i&lt;=b)
\n{
\n&lt;corpo del ciclo&gt;
\ni=i+c;
\n}
\n[\/code]<\/p>\n<\/div>\n

<\/pre>\n
\u00a0<\/span><\/div>\n","protected":false},"excerpt":{"rendered":"
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