Foreach in C++ and Java
Last Updated :
29 May, 2023
Foreach loop is used to iterate over the elements of a container (array, vectors, etc) quickly without performing initialization, testing, and increment/decrement. The working of foreach loops is to do something for every element rather than doing something n times. There is no foreach loop in C, but both C++ and Java support the foreach type of loop. In C++, it was introduced in C++ 11 and Java in JDK 1.5.0 The keyword used for foreach loop is “for” in both C++ and Java.
Syntax:
for (data_type variable_name : container_name) {
operations using variable_name
}
With the introduction of auto keyword in C++ and var keyword in Java, we no longer need to specify the data type for the variable in foreach loop. Type inference detects the data type of the container and automatically sets the same data type to the variable used for traversing.
The below code displays the use case of foreach loop for different containers along with auto/var keywords in C++/Java.
C++/Java Program for array:
C++
#include <iostream>
using namespace std;
int main()
{
int arr[] = { 10, 20, 30, 40 };
cout<<"Traversing the array with foreach using array's data type: ";
for (int x : arr)
cout<<x<<" ";
cout<<"\nTraversing the array with foreach using auto keyword : ";
for (auto x : arr)
cout<<x<<" ";
}
|
Java
public class Main {
public static void main(String[] args)
{
int arr[] = { 10, 20, 30, 40 };
System.out.print("Traversing the array with foreach using array's data type: ");
for (int x : arr)
System.out.print(x+" ");
System.out.print("\nTraversing the array with foreach using auto keyword : ");
for (var x : arr)
System.out.print(x+" ");
}
}
|
Output
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
C++ Program for vector:
C++
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<string> 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 << "\nTraversing the vector with foreach using "
"auto keyword : ";
for (auto v : value)
cout << v << " ";
return 0;
}
|
Output
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.
Java Program for ArrayList:
Java
import java.util.*;
class GFG {
public static void main(String[] args)
{
ArrayList<Integer> list = new ArrayList<>();
list.add(3);
list.add(24);
list.add(-134);
list.add(-2);
list.add(100);
for (int element : list) {
System.out.print(element + " ");
}
}
}
|
C++/Java Program for set:
C++
#include <iostream>
#include <set>
using namespace std;
int main() {
set<int> 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<<"\nTraversing the set with foreach using auto keyword : ";
for (auto v : value)
cout<<v<<" ";
return 0;
}
|
Java
import java.util.*;
public class GFG {
public static void main(String[] args)
{
Set<String> hash_Set = new HashSet<String>();
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("\nTraversing the set with foreach using auto keyword : ");
for (var hs : hash_Set) {
System.out.print(hs+" ");
}
}
}
|
Output
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
Note: We can use different data types in foreach for array, vector and set.
C++/Java Program for map:
C++14
#include <iostream>
#include <map>
using namespace std;
int main() {
map<int, string> mapExample;
mapExample.insert(pair<int, string>(1, "Geeks"));
mapExample.insert(pair<int, string>(2, "4"));
mapExample.insert(pair<int, string>(3, "Geeks"));
mapExample.insert(pair<int, string>(4, "Map"));
mapExample.insert(pair<int, string>(5, "Foreach"));
mapExample.insert(pair<int, string>(6, "Example"));
cout<<"Traversing the map with foreach using map's data type\n";
for (pair<int, string> mpEx : mapExample ) {
cout<<mpEx.first<<" "<<mpEx.second<<endl;
}
cout<<"\nTraversing the map with foreach using auto keyword\n";
for (auto mpEx : mapExample){
cout<<mpEx.first<<" "<<mpEx.second<<endl;
}
return 0;
}
|
Java
import java.io.*;
import java.util.Map;
import java.util.HashMap;
class GFG {
public static void main (String[] args) {
Map<Integer,String> gfg = new HashMap<Integer,String>();
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<Integer, String> entry : gfg.entrySet())
System.out.println(entry.getKey() + " " + entry.getValue());
System.out.println("\nTraversing the map with foreach using auto keyword");
for (var entry : gfg.entrySet())
System.out.println(entry.getKey() + " " + entry.getValue());
}
}
|
Output
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
Advantages of foreach loop:
- Makes the code more readable.
- Eliminates the errors of over-running or under-running the data.
Disadvantage of foreach loop:
- Cannot iterate over the elements in reverse order.
- Each and every element will be accessed, cannot skip any elements in between.
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