logo

Foreach in C++ und JAVA

Die foreach-Schleife wird verwendet, um die Elemente eines Containers (Array, Vektoren usw.) schnell zu durchlaufen, ohne eine Initialisierung, einen Test oder eine Inkrementierung/Dekrementierung durchzuführen. Foreach-Schleifen funktionieren, indem sie für jedes Element etwas tun, anstatt etwas n-mal auszuführen. Obwohl es in C keine foreach-Schleife gibt, wird sie von C++ und Java unterstützt. Es wurde erstmals in C++ in C++ 11 und in Java in JDK 1.5.0 eingeführt. Sowohl in C++ als auch in Java lautet das Schlüsselwort für die foreach-Schleife „for“.

Syntax

 for (data_type variable_name : container_type) { operations using variable_name } 

Dank der Einführung des Schlüsselworts auto in C++ und des Schlüsselworts var in Java müssen wir den Datentyp für Variablen in foreach-Schleifen nicht mehr angeben. Die Typinferenz erkennt den Datentyp des Containers und setzt die zum Durchlaufen verwendete Variable auf denselben Datentyp.

Der folgende Code demonstriert die Verwendung einer foreach-Schleife für verschiedene Container sowie die Schlüsselwörter 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&lt;<'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(&apos;Traversing the array with foreach using array&apos;s data type: &apos;); for (int x : arr) System.out.print(x+&apos; &apos;); // data type of x is set as int System.out.print(&apos;
Traversing the array with foreach using auto keyword : &apos;); for (var x : arr) System.out.print(x+&apos; &apos;); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the array with foreach using array&apos;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{&apos;This&apos;, &apos;is&apos;, &apos;foreach&apos;, &apos;example&apos;, &apos;using&apos;, &apos;vector.&apos;}; cout&lt;<'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&apos;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&lt;<'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(&apos;Geeks&apos;); hash_Set.add(&apos;For&apos;); hash_Set.add(&apos;Geeks&apos;); hash_Set.add(&apos;Foreach&apos;); hash_Set.add(&apos;Example&apos;); hash_Set.add(&apos;Set&apos;); System.out.print(&apos;Traversing the set with foreach using set&apos;s data type: &apos;); for(String hs : hash_Set) { System.out.print(hs+&apos; &apos;); } System.out.print(&apos;
Traversing the set with foreach using auto keyword : &apos;); for (var hs : hash_Set) { System.out.print(hs+&apos; &apos;); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set&apos;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, &apos;Geeks&apos;)); mapExample.insert(pair(2, &apos;4&apos;)); mapExample.insert(pair(3, &apos;Geeks&apos;)); mapExample.insert(pair(4, &apos;Map&apos;)); mapExample.insert(pair(5, &apos;Foreach&apos;)); mapExample.insert(pair(6, &apos;Example&apos;)); cout&lt;<'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, &apos;Geeks&apos;); gfg.put(2, &apos;4&apos;); gfg.put(3, &apos;Geeks&apos;); gfg.put(4, &apos;Map&apos;); gfg.put(5, &apos;Foreach&apos;); gfg.put(6, &apos;Example&apos;); System.out.println(&apos;Traversing the map with foreach using map&apos;s data type&apos;); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); System.out.println(&apos;
Traversing the map with foreach using auto keyword&apos;); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map&apos;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>

Ausgabe

 Traversing the array with foreach using array&apos;s data type: 10 20 30 40 Traversing the array with foreach using auto keyword : 10 20 30 40 

Vector C++-Programm:

 #include #include using namespace std; int main() { vector value{&apos;This&apos;, &apos;is&apos;, &apos;foreach&apos;, &apos;example&apos;, &apos;using&apos;, &apos;vector.&apos;}; cout&lt;<\'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&apos;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&lt;<\'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(&apos;Geeks&apos;); hash_Set.add(&apos;For&apos;); hash_Set.add(&apos;Geeks&apos;); hash_Set.add(&apos;Foreach&apos;); hash_Set.add(&apos;Example&apos;); hash_Set.add(&apos;Set&apos;); System.out.print(&apos;Traversing the set with foreach using set&apos;s data type: &apos;); for(String hs : hash_Set) { System.out.print(hs+&apos; &apos;); } System.out.print(&apos;
Traversing the set with foreach using auto keyword : &apos;); for (var hs : hash_Set) { System.out.print(hs+&apos; &apos;); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set&apos;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, &apos;Geeks&apos;)); mapExample.insert(pair(2, &apos;4&apos;)); mapExample.insert(pair(3, &apos;Geeks&apos;)); mapExample.insert(pair(4, &apos;Map&apos;)); mapExample.insert(pair(5, &apos;Foreach&apos;)); mapExample.insert(pair(6, &apos;Example&apos;)); cout&lt;<\'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, &apos;Geeks&apos;); gfg.put(2, &apos;4&apos;); gfg.put(3, &apos;Geeks&apos;); gfg.put(4, &apos;Map&apos;); gfg.put(5, &apos;Foreach&apos;); gfg.put(6, &apos;Example&apos;); System.out.println(&apos;Traversing the map with foreach using map&apos;s data type&apos;); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); System.out.println(&apos;
Traversing the map with foreach using auto keyword&apos;); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map&apos;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>

C++/Java-Set-Programm:

C++

 #include #include using namespace std; int main() { set value = {6, 2, 7, 4, 10, 5, 1}; cout&lt;<\'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(&apos;Geeks&apos;); hash_Set.add(&apos;For&apos;); hash_Set.add(&apos;Geeks&apos;); hash_Set.add(&apos;Foreach&apos;); hash_Set.add(&apos;Example&apos;); hash_Set.add(&apos;Set&apos;); System.out.print(&apos;Traversing the set with foreach using set&apos;s data type: &apos;); for(String hs : hash_Set) { System.out.print(hs+&apos; &apos;); } System.out.print(&apos;
Traversing the set with foreach using auto keyword : &apos;); for (var hs : hash_Set) { System.out.print(hs+&apos; &apos;); } } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the set with foreach using set&apos;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, &apos;Geeks&apos;)); mapExample.insert(pair(2, &apos;4&apos;)); mapExample.insert(pair(3, &apos;Geeks&apos;)); mapExample.insert(pair(4, &apos;Map&apos;)); mapExample.insert(pair(5, &apos;Foreach&apos;)); mapExample.insert(pair(6, &apos;Example&apos;)); cout&lt;<\'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, &apos;Geeks&apos;); gfg.put(2, &apos;4&apos;); gfg.put(3, &apos;Geeks&apos;); gfg.put(4, &apos;Map&apos;); gfg.put(5, &apos;Foreach&apos;); gfg.put(6, &apos;Example&apos;); System.out.println(&apos;Traversing the map with foreach using map&apos;s data type&apos;); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); System.out.println(&apos;
Traversing the map with foreach using auto keyword&apos;); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map&apos;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>

Ausgabe

 Traversing the set with foreach using set&apos;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 

Für Array, Vektor und Set können wir in foreach unterschiedliche Datentypen verwenden.

C++/Java Map-Programm:

C++

 #include #include using namespace std; int main() { map mapExample; mapExample.insert(pair(1, &apos;Geeks&apos;)); mapExample.insert(pair(2, &apos;4&apos;)); mapExample.insert(pair(3, &apos;Geeks&apos;)); mapExample.insert(pair(4, &apos;Map&apos;)); mapExample.insert(pair(5, &apos;Foreach&apos;)); mapExample.insert(pair(6, &apos;Example&apos;)); cout&lt;<\\'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, &apos;Geeks&apos;); gfg.put(2, &apos;4&apos;); gfg.put(3, &apos;Geeks&apos;); gfg.put(4, &apos;Map&apos;); gfg.put(5, &apos;Foreach&apos;); gfg.put(6, &apos;Example&apos;); System.out.println(&apos;Traversing the map with foreach using map&apos;s data type&apos;); for (Map.Entry entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); System.out.println(&apos;
Traversing the map with foreach using auto keyword&apos;); for (var entry : gfg.entrySet()) System.out.println(entry.getKey() + &apos; &apos; + entry.getValue()); } } </pre> <p> <strong>Output</strong> </p> <pre> Traversing the map with foreach using map&apos;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>

Ausgabe

 Traversing the map with foreach using map&apos;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 

Die Foreach-Schleife bietet folgende Vorteile:

  • Dies verbessert die Lesbarkeit des Codes.
  • Beseitigt die Möglichkeit von Datenüberschreitungs- oder -unterschreitungsfehlern.

Die Foreach-Schleife hat den folgenden Nachteil:

  • Es ist nicht möglich, die Elemente in umgekehrter Reihenfolge zu durchlaufen.
  • Auf jedes Element wird zugegriffen; Es werden keine Elemente dazwischen übersprungen.