Collapse All Levels Collapse Top Level Expand Top Level Expand All Levels
News Articles Recipes Beginner's Guide to C++ Lists
@hackingcpp RSS Feed About Privacy Home
    Beginner's Guide
    First Steps
    Input & Output
    Custom Types – Part 1
    Diagnostics
    Standard Library – Part 1
    Function Objects
    Standard Library – Part 2
    Code Organization
    Custom Types – Part 2
    Generic Programming
    Memory Management
    Software Design Basics

    Type System Basics Type System Basics Type Basics

    Declare Constants With const Constants: const const

    Type const variable_name = value;
    • value can't be changed once assigned
    • initial value can be dynamic (= set at runtime)
    int i = 0;
cin >> i;
int const k = i;  // "int constant"
k = 5;  //  COMPILER ERROR: k is const!

    Always declare variables as const if you don't need to change their values after the initial assignment!

    • avoids bugs: does not compile if you accidentally change the value later
    • helps understanding your code better: clearly communicates that the value will stay the same further down in the code
    • can improve performance (more compiler optimizations possible)

    Type Aliases using

    using NewType = OldType;  C++11

    typedef OldType NewType;  C++98

    using real = double;
using ullim = std::numeric_limits<unsigned long>;
using index_vector = std::vector<std::uint_least64_t>;

    Prefer the more powerful (we'll later see why) using over the outdated and ambiguous typedef!

    Type Deduction: auto C++11 auto

    auto variable = expression;
    • variable type deduced from right hand side of assignment
    • often more convenient, safer and future proof
    • also important for generic (type independent) programming
    auto i = 2;                 
auto u = 56u;               
auto d = 2.023;             
auto f = 4.01f;             
auto l = -78787879797878l;  

    auto x = 0 * i;         
auto y = i + d;             
auto z = f * d;
    int
unsigned int
double
float
long int

    x: int
y: double
z: double

    Constant Expressions: constexpr C++11 constexpr C++11 constexpr

    • must be computable at compile time
    • can be computed at runtime if not invoked in a constexpr context
    • all expressions inside a constexpr context must be constexpr themselves
    • constexpr functions may contain
      • C++11  nothing but one return statement
      • C++14  multiple statements
    // two simple functions:
constexpr int cxf (int i) { return i*2; }
          int foo (int i) { return i*2; }

    // OK '2' is a literal:constexpr int i = 2;       // OK '2' is a literal

    // OK, 'cxf' is constexpr:constexpr int j = cxf(5);  // OK, cxf is constexpr 
// OK, 'cxf' and i are constexpr:constexpr int k = cxf(i);  // OK, cxf and i are constexpr

              int x = 0;       // not constexpr
// non-constexpr context:          int l = cxf(x);  // OK// OK, not a constexpr context

    // constexpr contexts:
// constexpr int m = cxf( x );  // 
// constexpr int n = foo( 5 );  //
    Control Flow
    Beginner's Guide / First Steps
    Functions

    Last updated: 2019-11-09

    Comments…