Summary  
This chapter explains how to use nested for loops to perform iterations within iterations, enabling traversal of multi-dimensional data or generation of repeated patterns in code.

General domain of usage  
Pattern printing

A nested `for` loops are almost the same as a nested `while` loops. They allow you to create **a set of iterations within another set of iterations**, but in more convenient way. It is particularly useful when dealing with two-dimensional or multi-dimensional data structures with elements your want to **iterate** through.

You had a task that involved creating a rectangle in a console using three loops. As you already could guess there is a more straightforward and flexible way to accomplish this.

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Understanding nested loops may be challenging initially, but once you grasp the concept, it becomes easy. So, let's try to practice.

#define CATCH_CONFIG_MAIN
#include <catch2/catch.hpp>
#include <sstream>
#include <iostream>

void multiplicationTable(int size);

TEST_CASE("Multiplication table of size 1", "[multiplicationTable]") {
    std::ostringstream output;
    std::streambuf* oldCout = std::cout.rdbuf(output.rdbuf());

    multiplicationTable(1);

    std::cout.rdbuf(oldCout);

    std::string expected = R"(1 * 1 = 1

)";

    REQUIRE(output.str() == expected);
}

TEST_CASE("Multiplication table of size 2", "[multiplicationTable]") {
    std::ostringstream output;
    std::streambuf* oldCout = std::cout.rdbuf(output.rdbuf());

    multiplicationTable(2);

    std::cout.rdbuf(oldCout); // Ð²Ð¾ÑÑÑÐ°Ð½Ð¾Ð²Ð¸Ð¼ cout

    std::string expected = R"(1 * 1 = 1
1 * 2 = 2

2 * 1 = 2
2 * 2 = 4

)";

    REQUIRE(output.str() == expected);
}

TEST_CASE("Multiplication table of size 3", "[multiplicationTable]") {
    std::ostringstream output;
    std::streambuf* oldCout = std::cout.rdbuf(output.rdbuf());

    multiplicationTable(3);

    std::cout.rdbuf(oldCout);

    std::string expected = R"(1 * 1 = 1
1 * 2 = 2
1 * 3 = 3

2 * 1 = 2
2 * 2 = 4
2 * 3 = 6

3 * 1 = 3
3 * 2 = 6
3 * 3 = 9

)";

    REQUIRE(output.str() == expected);
}

TEST_CASE("Multiplication table of size 5", "[multiplicationTable]") {
    std::ostringstream output;
    std::streambuf* oldCout = std::cout.rdbuf(output.rdbuf());

    multiplicationTable(5);

    std::cout.rdbuf(oldCout);

    std::string expected = R"(1 * 1 = 1
1 * 2 = 2
1 * 3 = 3
1 * 4 = 4
1 * 5 = 5

2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10

3 * 1 = 3
3 * 2 = 6
3 * 3 = 9
3 * 4 = 12
3 * 5 = 15

4 * 1 = 4
4 * 2 = 8
4 * 3 = 12
4 * 4 = 16
4 * 5 = 20

5 * 1 = 5
5 * 2 = 10
5 * 3 = 15
5 * 4 = 20
5 * 5 = 25

)";

    REQUIRE(output.str() == expected);
}

test.cpp

C++ Loops from scratch. Master one of the fundamental building blocks for programming. This course is perfect for beginners and those looking to solidify their understanding of loops.

Dive into the fundamental concept of while loops in C++. This section will equip you with a deep understanding and knowledge of how while loops work, providing you with the skills necessary to effectively use them in your programs.

Challenge: How to Work with Nested For Loops in C++

Solution