Lasagna

Basics

To set off the C++ journey we are starting with variables, function calls, and comments.

Comments

Comments come in two flavors: single- and multi-line. Everything that comes after // on the same line is ignored by the compiler. Multi-line comments are also known as C-style comments. They are surrounded by /* and */. Anything that comes between these will be ignored as well.

Variables

C++ is a typed language. All types need to be known at compile time, and you generally need to state them explicitly. A variable's type cannot change. An integer variable with the name years can be declared like this:

int years;

It is good practice to initialize variables upon declaration. C++ offers different mechanisms to do so. The version with the curly braces is more in line with modern C++, but the equal-sign version is also very common.

int tomatoes{80};
int potatoes = 40;

Arithmetic Operations

Arithmetic operators like *, +, or - can be part of an expression like 3 * 2 or tomatoes + potatoes.

Updating Variables

You can reassign variables, as long as they keep their type:

tomatoes = tomatoes - 5; // tomatoes is now 75
potatoes = (32 * 2) + 11; // potatoes is now 75 as well

Functions

Functions have a name, a return type and a (possibly empty) parameter list. An example of a function named always_fortyseven that would always return 47 would look like this:

int always_fortyseven() {
    return 47;
}

Here is vip_fee, which has one parameter:

int vip_fee(int standard_fee) {
    /*
    vip_fee calculates the vip fee based on the standard_fee.
    */
    int vip_multi{3};
    return standard_fee * vip_multi;
}

Or total_fee, a function with three parameters and a call to another function.

int total_fee(int vips, int adults, int kids) {
    /*
    total_fee calculates the total price for a group of VIP and adult guests with kids.
    Kids get a flat discount on the standard fee.
    VIP guest fees are calculated by calling vip_fee.
    */
    int standard_fee{30};
    int kids_discount{15};

    int kids_total_fee = kids * (standard_fee - kids_discount);
    int vips_total_fee = vips * vip_fee(standard_fee);
    int adult_total_fee = adults * standard_fee;

    return vips_total_fee + adult_total_fee + kids_total_fee;
}

Functions in C++ do not return the value of the last statement like in some other languages. The return keyword is required for the code to compile.

Whitespace

Whitespace is used for formatting source code and includes spaces, tabs, or newlines. As the compiler ignores unnecessary whitespace, you can use it to structure your code. Smart use of whitespace can improve the readability of your code. There are different formatting standards, but these are all conventional and not enforced by the compiler.

// Formatting makes it easier to find bugs

int eggs_yolks =  3;
int      yeast = 15;

int flour=500;int sugar=200;// compact, but difficult to read