Foreach-loopen används för att snabbt iterera över elementen i en behållare (matris, vektorer, etc.) utan att utföra initialisering, testning eller ökning/minskning. Foreach loops fungerar genom att göra något för varje element istället för att göra något n gånger. Även om det inte finns någon foreach loop i C, stöds den av C++ och Java. Det introducerades först i C++ i C++ 11 och i Java i JDK 1.5.0. I både C++ och Java är nyckelordet för foreach loop 'for'.
Syntax
for (data_type variable_name : container_type) { operations using variable_name } Vi behöver inte längre specificera datatypen för variabler i varje loop tack vare introduktionen av auto-nyckelordet i C++ och nyckelordet var i Java. Typinferens upptäcker datatypen för behållaren och ställer in variabeln som används för att korsa till samma datatyp.
Koden nedan visar användningen av en foreach loop för olika behållare, såväl som auto/var nyckelord i 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> Produktion
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
Vector C++-program:
#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> C++/Java Set Program:
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> Produktion
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
För array, vektor och uppsättning kan vi använda olika datatyper i varje.
C++/Java kartprogram:
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> Produktion
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
För varje slinga har följande fördelar:
- Detta förbättrar kodens läsbarhet.
- Tar bort risken för dataöver- eller underkörningsfel.
Foreach loop har följande nackdel:
- Det är inte möjligt att iterera över elementen i omvänd ordning.
- Varje element kommer att nås; inga element däremellan kommer att hoppas över.