Cracking C++ (8): Loops, Initializer List

Loops

while loop

• repeat the code until expression evaluates to true
  • unless break is used to immediately get out of the loop
  • unless continue is used to return to the top and reevaluate the expression

int i { 0 };
while (i < 5) {
	cout << "Hello World" << endl;
    ++i;
}

do/while loop

• code execution comes first, then evaluates expression to guarantee at least one code execution

int i { 100 };
do {
	cout << "Hello World" << endl;
    ++i;
} while (i < 5);

for loop

• can be converted into while loop and vice versa
• for (starting expression; end condition; statement to execute at the end){}

Range-based for loop

• used for easy iteration over elements in a container (e.g. C-style array, initializer lists, any type that has begin() and end() like array, vector

array arr { 1, 2, 3, 4 };
for (int i : arr) { cout << i << endl; }

• from C++20, we can use initializers with range-based for loop, similar to initializers in if and switch

for (array arr { 1, 2, 3, 4 }; int i: arr) { cout << i << endl; }

Initializer Lists

• defined in <initializer_list> - make it easy to write functions that accept a variable number of arguments
• class template - specify types of elements in the lists in <>

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

int makeSum(initializer_list<int> values) {
    int total { 0 };
    for (int value : values) {
        total += value;
    }
    return total;
}

int a { makeSum({ 1, 2, 3 }) }; 
int b { makeSum({ 10, 20, 30, 40, 50, 60 }) };

• type-safe, so all elements in the list has to be of the same type