Module 00 is all about getting acquainted with CPP basics: Namespaces, classes, member functions, stdio streams, initialization lists, static, const, and so on.
📢 Ex00 - Megaphone 📣
A really straightforward exercice to practice with the iostream library and std::cout.
📑 Ex01 - Phonebook ☎️
Some issues I got and ressources which helped me solve them:
Example:
std::string input;
std::cin >> input;
// If the input typed by the user is "Hello World", input will be equal to "Hello" and not "Hello World".This issue was fixed with std::getline, which reads all the characters from an input stream and puts them onto a string.
#include <iostream>
#include <string>
int main() {
// Declare a firstname (String)
std::string firstname;
std::cout << "What is your firstname ?" << std::endl;
// Get the input from std::cin and store into firstname
std::getline(std::cin, firstname);
return 0;
}Combining std::cin and std::getline
If you try and run the following code, you will see that the firstname getline will be skipped and the "lastname" prompt will be displayed. This is because of std::cin's usage just above.
int main(void)
{
char *input;
std::cout << "Please enter a one-word command" << std::endl;
std::cin >> input; // Here is where std::cin precedes the usage of std::getline()
if (input == "ADD")
{
std::string firstname;
std::cout << "Enter your firstname" << std::endl;
std::getline(std::cin, firstname);
std::cout << "First name registered: " << firstname << std::endl;
std::string lastname;
std::cout << "Enter your lastname" << std::endl;
std::getline(std::cin, lastname);
std::cout << "Last name registered: " << lastname << std::endl;
}
return (0);
}Explanation:
"std::getline() does not ignore any leading white-space / newline characters. Because of this, if you call std::cin >> var; just before getline(), there will be a newline still remaining in the input stream, after reading the input variable. So, if you call getline() immediately after cin, you will get a newline instead, since it is the first character in the input stream! To avoid this, simply add a dummy std::getline() to consume this new-line character!"
Ressource How to use getline
Catching errors with std::cin.fail()
In this exercise, you will have to ask the user's input several times, in order to add a contact to the phonebook. I used std::getline() for strings and std::cin for the phone number, because we were dealing with (long) ints.
However, how do you prevent the user from entering some alpha characters and crashing the program?
Well, you don't, buuuut you can catch the error with the method std::cin.fail():
int main(void)
{
long int phonenumber;
std::cin >> phonenumber;
if (std::cin.fail() == true) // For example if the input is invalid because it is not the right type
{
std::cin.clear(); // Clears the error flag from cin.fail();
std::cin.ignore(); // Ignores the fail that just happened
std::cout << "Invalid input ! Try again." << std::endl;
std::cin >> phonenumber;
}
std::cout << "Good ! Your phonenumber is : " << phonenumber << std::endl;
}
Ressource How to use cin.fail() in c++ properly
std::cin.ignore tip :
If you try and keep asking for the user's input while the input given is wrong/triggers std::cin.fail(), your error_msg will repeat itself for as many times as there are chars in the input's string. To avoid this, use the argument:
// will ignore any other input that is not an integer and will skip to the new line.
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); Preventing the program from crashing with a EOF
If the user's (or any tester) tries to end the program with CTRL+D while we are in the std::cin/getline stage, you will have a never-ending loop of your prompt. To catch this signal, use the std::cin.eof() method:
void askForNickname(Contact *contact)
{
std::string nickname;
std::cout << BLUE << "📜 May I ask for your nickname?" << RESET << std::endl;
std::getline(std::cin, nickname);
if (std::cin.eof() == true) // If the program catches an EOF, exit safely the program
exit(0);
while (nickname.empty()) // aka "while the user keep hitting the return key"
{
std::cout << BLUE << "📜 Don't be shy! Please speak louder." << RESET << std::endl;
std::getline(std::cin, nickname);
if (std::cin.eof() == true)
exit(0);
}
contact->setNickname(nickname);
return ;
}#define SUCCESS 0
std::string input;
std::string add_command("ADD");
std::getline(std::cin, input);
std::cout << add_command.compare(input) == SUCCESS ? "OK" : "KO" << std::endl;
// is the same as:
std::cout << (input == "ADD") ? "OK" : "KO" << std::endl;No need to code formatting functions from scratch with the iomanip library!
| Function | Use | Link |
|---|---|---|
| std::right | Modifies the positioning of the fill characters in an output stream. | Here |
| std::setw(int n) | Sets the field width to be used on output operations. | Here |
Useful member functions to truncate the strings according to the subject's needs:
"Si le texte dépasse la largeur de la colonne, il faut le tronquer et remplacer le dernier caractère affiché par un point (’.’)."
std::string trunc(std::string info)
{
if (info.length() > 10)
{
info.resize(9); // keeps the first 9th chars of the string
info.append("."); // appends a dot as required to the precedently modified string
}
return info;
}All std::string member functions here.
float fmod(float a, float b) => retourne le reste d'une division de a par b (ici, toujours 1) // instant nerd : difference remainder v. fmod = la façon dont on arrondit /* remainder : x - r * y, où r est le résultat de x/y, arrondi à la valeur entière la plus proche fmod : x _ t * y, où t est le résultat tronqué (aka arrondi vers 0) de x/y
EXEMPLE :
double x = 5.1, y = 3;
double result = remainder(x, y); => output is -0.9 (car 5.1/3 = 1.7, et là on arrondit à 2. Donc 5.1 - 2 * 3 = -0.9)
double result2 = fmod(x, y); => output is 2.1
Source: https://stackoverflow.com/questions/25734144/difference-between-c-functions-remainder-and-fmod