Il ciclo foreach viene utilizzato per scorrere rapidamente gli elementi di un contenitore (array, vettori, ecc.) senza eseguire inizializzazione, test o incremento/decremento. I cicli Foreach funzionano facendo qualcosa per ciascun elemento anziché fare qualcosa n volte. Sebbene non sia presente un ciclo foreach in C, è supportato da C++ e Java. È stato introdotto per la prima volta in C++ in C++ 11 e in Java in JDK 1.5.0. Sia in C++ che in Java, la parola chiave per il ciclo foreach è 'for'.
Sintassi
for (data_type variable_name : container_type) { operations using variable_name } Non abbiamo più bisogno di specificare il tipo di dati per le variabili nei cicli foreach grazie all'introduzione della parola chiave auto in C++ e della parola chiave var in Java. L'inferenza del tipo rileva il tipo di dati del contenitore e imposta la variabile utilizzata per l'attraversamento sullo stesso tipo di dati.
Il codice seguente dimostra l'uso di un ciclo foreach per vari contenitori, nonché le parole chiave auto/var in C++/Java.
C++
// C++ program to demonstrate use of foreach for array #include using namespace std; int main() { int arr[] = { 10, 20, 30, 40 }; // Printing elements of an array using // foreach loop // Here, int is the data type, x is the variable name // and arr is the array for which we want to iterate foreach cout<<'traversing the array with foreach using array's data type: '; for (int x : arr) cout<<x<<' type of is set as int cout<<'
traversing auto keyword (auto } < pre> <h3>JAVA</h3> <pre> // Java program to demonstrate use of foreach public class Main { public static void main(String[] args) { // Declaring 1-D array with size 4 int arr[] = { 10, 20, 30, 40 }; // Printing elements of an array using // foreach loop // Here, int is the data type, x is the variable name // and arr is the array for which we want to iterate foreach System.out.print('Traversing the array with foreach using array's data type: '); for (int x : arr) System.out.print(x+' '); // data type of x is set as int System.out.print('
Traversing the array with foreach using auto keyword : '); for (var x : arr) System.out.print(x+' '); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the array with foreach using array's data type: 10 20 30 40 Traversing the array with foreach using auto keyword : 10 20 30 40 </pre> <h3>Vector C++ programme:</h3> <pre> #include #include using namespace std; int main() { vector value{'This', 'is', 'foreach', 'example', 'using', 'vector.'}; cout<<'traversing the vector with foreach using vector's data type: '; for (string v : value) { cout<<v<<' } cout<<'
traversing auto keyword (auto return 0; < pre> <p> <strong>Output</strong> </p> <pre> Traversing the vector with foreach using vector's data type: This is foreach example using vector. Traversing the vector with foreach using auto keyword : This is foreach example using vector. </pre> <h2>C++/Java Set Program:</h2> <h3>C++</h3> <pre> #include #include using namespace std; int main() { set value = {6, 2, 7, 4, 10, 5, 1}; cout<<'traversing the set with foreach using set's data type: '; for (int v : value) { cout<<v<<' } cout<<'
traversing auto keyword (auto return 0; < pre> <h3>JAVA</h3> <pre> import java.util.*; public class GFG { public static void main(String[] args) { Set hash_Set = new HashSet(); hash_Set.add('Geeks'); hash_Set.add('For'); hash_Set.add('Geeks'); hash_Set.add('Foreach'); hash_Set.add('Example'); hash_Set.add('Set'); System.out.print('Traversing the set with foreach using set's data type: '); for(String hs : hash_Set) { System.out.print(hs+' '); } System.out.print('
Traversing the set with foreach using auto keyword : '); for (var hs : hash_Set) { System.out.print(hs+' '); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set's data type: 1 2 4 5 6 7 10 Traversing the set with foreach using auto keyword : 1 2 4 5 6 7 10 </pre> <p>For array, vector, and set, we can use different data types in foreach.</p> <h2>C++/Java Map Program:</h2> <h3>C++</h3> <pre> #include #include using namespace std; int main() { map mapExample; mapExample.insert(pair(1, 'Geeks')); mapExample.insert(pair(2, '4')); mapExample.insert(pair(3, 'Geeks')); mapExample.insert(pair(4, 'Map')); mapExample.insert(pair(5, 'Foreach')); mapExample.insert(pair(6, 'Example')); cout<<'traversing the map with foreach using map's data type
'; for (pair mpex : mapexample ) { cout<<mpex.first<<' '<<mpex.second<<endl; } cout<<'
traversing auto keyword
'; (auto mapexample){ return 0; < pre> <h3>JAVA</h3> <pre> import java.io.*; import java.util.Map; import java.util.HashMap; class GFG { public static void main (String[] args) { Map gfg = new HashMap(); gfg.put(1, 'Geeks'); gfg.put(2, '4'); gfg.put(3, 'Geeks'); gfg.put(4, 'Map'); gfg.put(5, 'Foreach'); gfg.put(6, 'Example'); System.out.println('Traversing the map with foreach using map's data type'); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); System.out.println('
Traversing the map with foreach using auto keyword'); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map's data type 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example Traversing the map with foreach using auto keyword 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example </pre> <h3>Foreach loop has the following advantages:</h3> <ul> <li>This improves the readability of the code.</li> <li>Removes the possibility of data over- or under-running errors.</li> </ul> <h3>Foreach loop has the following disadvantage:</h3> <ul> <li>It is not possible to iterate over the elements in reverse order.</li> <li>Every element will be accessed; no elements in between will be skipped.</li> </ul> <hr></'traversing></pre></'traversing></pre></'traversing></pre></'traversing> Produzione
Traversing the array with foreach using array's data type: 10 20 30 40 Traversing the array with foreach using auto keyword : 10 20 30 40
Programma vettoriale C++:
#include #include using namespace std; int main() { vector value{'This', 'is', 'foreach', 'example', 'using', 'vector.'}; cout<<\'traversing the vector with foreach using vector\'s data type: \'; for (string v : value) { cout<<v<<\' } cout<<\'
traversing auto keyword (auto return 0; < pre> <p> <strong>Output</strong> </p> <pre> Traversing the vector with foreach using vector's data type: This is foreach example using vector. Traversing the vector with foreach using auto keyword : This is foreach example using vector. </pre> <h2>C++/Java Set Program:</h2> <h3>C++</h3> <pre> #include #include using namespace std; int main() { set value = {6, 2, 7, 4, 10, 5, 1}; cout<<\'traversing the set with foreach using set\'s data type: \'; for (int v : value) { cout<<v<<\' } cout<<\'
traversing auto keyword (auto return 0; < pre> <h3>JAVA</h3> <pre> import java.util.*; public class GFG { public static void main(String[] args) { Set hash_Set = new HashSet(); hash_Set.add('Geeks'); hash_Set.add('For'); hash_Set.add('Geeks'); hash_Set.add('Foreach'); hash_Set.add('Example'); hash_Set.add('Set'); System.out.print('Traversing the set with foreach using set's data type: '); for(String hs : hash_Set) { System.out.print(hs+' '); } System.out.print('
Traversing the set with foreach using auto keyword : '); for (var hs : hash_Set) { System.out.print(hs+' '); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set's data type: 1 2 4 5 6 7 10 Traversing the set with foreach using auto keyword : 1 2 4 5 6 7 10 </pre> <p>For array, vector, and set, we can use different data types in foreach.</p> <h2>C++/Java Map Program:</h2> <h3>C++</h3> <pre> #include #include using namespace std; int main() { map mapExample; mapExample.insert(pair(1, 'Geeks')); mapExample.insert(pair(2, '4')); mapExample.insert(pair(3, 'Geeks')); mapExample.insert(pair(4, 'Map')); mapExample.insert(pair(5, 'Foreach')); mapExample.insert(pair(6, 'Example')); cout<<\'traversing the map with foreach using map\'s data type
\'; for (pair mpex : mapexample ) { cout<<mpex.first<<\' \'<<mpex.second<<endl; } cout<<\'
traversing auto keyword
\'; (auto mapexample){ return 0; < pre> <h3>JAVA</h3> <pre> import java.io.*; import java.util.Map; import java.util.HashMap; class GFG { public static void main (String[] args) { Map gfg = new HashMap(); gfg.put(1, 'Geeks'); gfg.put(2, '4'); gfg.put(3, 'Geeks'); gfg.put(4, 'Map'); gfg.put(5, 'Foreach'); gfg.put(6, 'Example'); System.out.println('Traversing the map with foreach using map's data type'); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); System.out.println('
Traversing the map with foreach using auto keyword'); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map's data type 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example Traversing the map with foreach using auto keyword 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example </pre> <h3>Foreach loop has the following advantages:</h3> <ul> <li>This improves the readability of the code.</li> <li>Removes the possibility of data over- or under-running errors.</li> </ul> <h3>Foreach loop has the following disadvantage:</h3> <ul> <li>It is not possible to iterate over the elements in reverse order.</li> <li>Every element will be accessed; no elements in between will be skipped.</li> </ul> <hr></\'traversing></pre></\'traversing></pre></\'traversing> Programma C++/Java Set:
C++
#include #include using namespace std; int main() { set value = {6, 2, 7, 4, 10, 5, 1}; cout<<\'traversing the set with foreach using set\'s data type: \'; for (int v : value) { cout<<v<<\' } cout<<\'
traversing auto keyword (auto return 0; < pre> <h3>JAVA</h3> <pre> import java.util.*; public class GFG { public static void main(String[] args) { Set hash_Set = new HashSet(); hash_Set.add('Geeks'); hash_Set.add('For'); hash_Set.add('Geeks'); hash_Set.add('Foreach'); hash_Set.add('Example'); hash_Set.add('Set'); System.out.print('Traversing the set with foreach using set's data type: '); for(String hs : hash_Set) { System.out.print(hs+' '); } System.out.print('
Traversing the set with foreach using auto keyword : '); for (var hs : hash_Set) { System.out.print(hs+' '); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set's data type: 1 2 4 5 6 7 10 Traversing the set with foreach using auto keyword : 1 2 4 5 6 7 10 </pre> <p>For array, vector, and set, we can use different data types in foreach.</p> <h2>C++/Java Map Program:</h2> <h3>C++</h3> <pre> #include #include using namespace std; int main() { map mapExample; mapExample.insert(pair(1, 'Geeks')); mapExample.insert(pair(2, '4')); mapExample.insert(pair(3, 'Geeks')); mapExample.insert(pair(4, 'Map')); mapExample.insert(pair(5, 'Foreach')); mapExample.insert(pair(6, 'Example')); cout<<\'traversing the map with foreach using map\'s data type
\'; for (pair mpex : mapexample ) { cout<<mpex.first<<\' \'<<mpex.second<<endl; } cout<<\'
traversing auto keyword
\'; (auto mapexample){ return 0; < pre> <h3>JAVA</h3> <pre> import java.io.*; import java.util.Map; import java.util.HashMap; class GFG { public static void main (String[] args) { Map gfg = new HashMap(); gfg.put(1, 'Geeks'); gfg.put(2, '4'); gfg.put(3, 'Geeks'); gfg.put(4, 'Map'); gfg.put(5, 'Foreach'); gfg.put(6, 'Example'); System.out.println('Traversing the map with foreach using map's data type'); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); System.out.println('
Traversing the map with foreach using auto keyword'); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map's data type 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example Traversing the map with foreach using auto keyword 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example </pre> <h3>Foreach loop has the following advantages:</h3> <ul> <li>This improves the readability of the code.</li> <li>Removes the possibility of data over- or under-running errors.</li> </ul> <h3>Foreach loop has the following disadvantage:</h3> <ul> <li>It is not possible to iterate over the elements in reverse order.</li> <li>Every element will be accessed; no elements in between will be skipped.</li> </ul> <hr></\'traversing></pre></\'traversing> Produzione
Traversing the set with foreach using set's data type: 1 2 4 5 6 7 10 Traversing the set with foreach using auto keyword : 1 2 4 5 6 7 10
Per array, vettore e set, possiamo utilizzare diversi tipi di dati in foreach.
Programma mappa C++/Java:
C++
#include #include using namespace std; int main() { map mapExample; mapExample.insert(pair(1, 'Geeks')); mapExample.insert(pair(2, '4')); mapExample.insert(pair(3, 'Geeks')); mapExample.insert(pair(4, 'Map')); mapExample.insert(pair(5, 'Foreach')); mapExample.insert(pair(6, 'Example')); cout<<\\'traversing the map with foreach using map\\'s data type
\\'; for (pair mpex : mapexample ) { cout<<mpex.first<<\\' \\'<<mpex.second<<endl; } cout<<\\'
traversing auto keyword
\\'; (auto mapexample){ return 0; < pre> <h3>JAVA</h3> <pre> import java.io.*; import java.util.Map; import java.util.HashMap; class GFG { public static void main (String[] args) { Map gfg = new HashMap(); gfg.put(1, 'Geeks'); gfg.put(2, '4'); gfg.put(3, 'Geeks'); gfg.put(4, 'Map'); gfg.put(5, 'Foreach'); gfg.put(6, 'Example'); System.out.println('Traversing the map with foreach using map's data type'); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); System.out.println('
Traversing the map with foreach using auto keyword'); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + ' ' + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map's data type 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example Traversing the map with foreach using auto keyword 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example </pre> <h3>Foreach loop has the following advantages:</h3> <ul> <li>This improves the readability of the code.</li> <li>Removes the possibility of data over- or under-running errors.</li> </ul> <h3>Foreach loop has the following disadvantage:</h3> <ul> <li>It is not possible to iterate over the elements in reverse order.</li> <li>Every element will be accessed; no elements in between will be skipped.</li> </ul> <hr></\\'traversing> Produzione
Traversing the map with foreach using map's data type 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example Traversing the map with foreach using auto keyword 1 Geeks 2 4 3 Geeks 4 Map 5 Foreach 6 Example
Ogni ciclo presenta i seguenti vantaggi:
- Ciò migliora la leggibilità del codice.
- Elimina la possibilità di errori di sovraccarico o sottoesecuzione dei dati.
Ogni ciclo presenta il seguente svantaggio:
- Non è possibile scorrere gli elementi in ordine inverso.
- Si accederà a ogni elemento; nessun elemento intermedio verrà saltato.