for-each Loop in C++

 

The for-each loop (also known as range-based for loop) in C++ is a simpler and more convenient way to iterate over elements in containers like arrays, vectors, or other collections. It was introduced in C++11 to make looping through elements more intuitive and readable.

This type of loop iterates over each element in a container without explicitly using an index.

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1️⃣ Syntax of for-each Loop:

for (datatype element : container) {
    // Code to process each element
}

• datatype: The type of the element in the container (e.g., int, char, float).
• element: A temporary variable that represents each individual element in the container during each iteration.
• container: The collection you are iterating over (e.g., an array, vector, or any other container).

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2️⃣ Example: for-each Loop with Array

Here’s an example of using a for-each loop to print all elements of an array:

#include <iostream>
using namespace std;

int main() {
    int numbers[] = {1, 2, 3, 4, 5};

    // for-each loop to print each element in the array
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Explanation:

• The loop iterates over each element in the numbers array, and num takes the value of each element one by one.
• The elements are printed out without needing to manage the index manually.

Output:

1 2 3 4 5

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3️⃣ Example: for-each Loop with Vector

The for-each loop works not just with arrays, but also with other containers such as vector. Here's an example using a vector:

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // for-each loop to print each element in the vector
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Explanation:

• This example demonstrates iterating over a vector container using the for-each loop.
• The loop goes through each element of the vector and prints it.

Output:

10 20 30 40 50

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4️⃣ Example: for-each Loop with String

You can also use the for-each loop to iterate over characters in a string:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string text = "Hello";

    // for-each loop to print each character in the string
    for (char c : text) {
        cout << c << " ";
    }

    return 0;
}

Explanation:

• In this case, the loop iterates through each character in the string text, printing them one by one.

Output:

H e l l o

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5️⃣ Using const with for-each Loop

If you do not need to modify the elements while iterating, it's a good practice to use the const keyword to ensure the elements are not accidentally changed:

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // for-each loop with const to avoid modifying elements
    for (const int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Explanation:

• Here, const int num ensures that the elements of the vector cannot be modified within the loop.
• This is useful when you want to guarantee that the elements remain unchanged.

Output:

10 20 30 40 50

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6️⃣ Using Reference in for-each Loop

If you want to modify the elements of the container within the loop, you can use references:

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> numbers = {10, 20, 30, 40, 50};

    // for-each loop with reference to modify elements
    for (int& num : numbers) {
        num *= 2;  // Multiply each element by 2
    }

    // Print modified elements
    for (int num : numbers) {
        cout << num << " ";
    }

    return 0;
}

Explanation:

• The int& num ensures that the loop variable num is a reference to the actual element in the container.
• This allows you to modify the elements inside the loop (in this case, multiplying them by 2).

Output:

20 40 60 80 100

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7️⃣ Limitations of for-each Loop:

• No index access: Unlike traditional for loops, you cannot access the index of the current element directly in a for-each loop.
• Non-modifiable elements: If you use const, you cannot modify the container's elements.
• Works only with containers: The for-each loop can only be used with iterable containers, like arrays, vectors, or lists.

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8️⃣ Key Points to Remember:

• The for-each loop is simpler and cleaner than traditional for loops when you don’t need to use the index.
• It's ideal for iterating over containers (arrays, vectors, sets, maps, etc.) without manually managing indices.
• You can use references if you need to modify elements within the loop.

Would you like to see more advanced examples, such as iterating over a map or performing specific actions on elements during iteration?