What is concatenation and when will it be useful?

Answer 1

Concatenation is the joining of two vectors to produce a new vector. The new vector simply appends one vector to the other. A vector is an array of variables of the same type. Concatenation is most commonly used to join two strings together (string concatenation). A string is simply an array of type char.

Answer 2

Concatenation literally means connecting or linking objects in series. Concatenation is useful in programming when you wish to join two separate objects together to produce a new object, where the new object holds a copy of the first object immediately followed by a copy of the second object. It's a bit like an append operation, but an append changes the first object so that it combines both objects, whereas concatenation produces an entirely new object.

Example:
std::string s1 {"hello "};std::string s2 {"world"};

std::string s3 {s1 + s2}; // concatenation (creates a new string from the "sum" of both strings)

s1 += s2; // append s2 to s1 (changes s1, same as invoking s1.append (s2))

assert (s1==s3); // prove equivalence