Apart from the generic looping techniques, such as “for, while and do-while”, C++ in its language also allows us to use another functionality which solves the same purpose termed “for-each” loops. This loop accepts a function which executes over each of the container elements. This loop is defined in the header file “algorithm”, and hence has to be included for successful operation of this loop.
- Why to use for_each?
- It is versatile, i.e can work with any container.
- It reduces chances of errors one can commit using generic for loop
- It makes code more readable
- for_each loops improve overall performance of code
Syntax:
for_each (InputIterator first, InputIterator last, Function fn) strt_iter : The beginning position from where function operations has to be executed. last_iter : This ending position till where function has to be executed. fnc/obj_fnc : The 3rd argument is a function or an object function which operation would be applied to each element.
// C++ code to demonstrate the // working of for_each loop #include<iostream> #include<vector> #include<algorithm> using namespace std; // helper function 1 void printx2(int a) { cout << a * 2 << " "; } // helper function 2 // object type function struct Class2 { void operator() (int a) { cout << a * 3 << " "; } } ob1; int main() { // initializing array int arr[5] = { 1, 5, 2, 4, 3 }; cout << "Using Arrays:" << endl; // printing array using for_each // using function cout << "Multiple of 2 of elements are : "; for_each(arr, arr + 5, printx2); cout << endl; // printing array using for_each // using object function cout << "Multiple of 3 of elements are : "; for_each(arr, arr + 5, ob1); cout << endl; // initializing vector vector<int> arr1 = { 4, 5, 8, 3, 1 }; cout << "Using Vectors:" << endl; // printing array using for_each // using function cout << "Multiple of 2 of elements are : "; for_each(arr1.begin(), arr1.end(), printx2); cout << endl; // printing array using for_each // using object function cout << "Multiple of 3 of elements are : "; for_each(arr1.begin(), arr1.end(), ob1); cout << endl; } |
Output:
Using Arrays: Multiple of 2 of elements are : 2 10 4 8 6 Multiple of 3 of elements are : 3 15 6 12 9 Using Vectors: Multiple of 2 of elements are : 8 10 16 6 2 Multiple of 3 of elements are : 12 15 24 9 3
Exceptions and for_each
In the cases of exceptions, if the function throws an exception, for_each loop will also throw an exception and break/terminate the loop.
// C++ code to demonstrate the working // of for_each with Exception #include<iostream> #include<vector> #include<algorithm> using namespace std; // Helper function 1 void printx2(int a) { cout << a * 2 << " "; if ( a % 2 == 0) { throw a; } } // Helper function 2 // object type function struct Class2 { void operator() (int a) { cout << a * 3 << " "; if ( a % 2 == 0) { throw a; } } } ob1; int main() { // Initializing array int arr[5] = { 1, 5, 2, 4, 3 }; cout << "Using Array" << endl; // Printing Exception using for_each // using function try { for_each(arr, arr + 5, printx2); } catch(int i) { cout << "\nThe Exception element is : " << i ; } cout << endl; // Printing Exception using for_each // using object function try { for_each(arr, arr + 5, ob1); } catch(int i) { cout << "\nThe Exception element is : " << i ; } // Initializing vector vector<int> arr1 = { 1, 3, 6, 5, 1 }; cout << "\nUsing Vector" << endl; // Printing Exception using for_each // using function try { for_each(arr1.begin(), arr1.end(), printx2); } catch(int i) { cout << "\nThe Exception element is : " << i ; } cout << endl; // printing Exception using for_each // using object function try { for_each(arr1.begin(), arr1.end(), ob1); } catch(int i) { cout << "\nThe Exception element is : " << i ; } } |
Output:
Using Array 2 10 4 The Exception element is : 2 3 15 6 The Exception element is : 2 Using Vector 2 6 12 The Exception element is : 6 3 9 18 The Exception element is : 6
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