C++ - Types & Keywords

Overview

Estimated time: 35–50 minutes

Learn the core builtin types, their sizes and limits, numeric and character literals, and get familiar with commonly used keywords in modern C++.

Learning Objectives

• Identify fundamental types (bool, char variants, integer, floating-point).
• Print sizes and limits using sizeof and numeric_limits.
• Recognize key language keywords grouped by purpose.

Prerequisites

• C++ - Syntax & Basics

Fundamental types and sizes

#include <iostream>
#include <limits>
int main(){
  std::cout << "sizeof(bool)=" << sizeof(bool) << "\n";
  std::cout << "sizeof(char)=" << sizeof(char) << "\n";
  std::cout << "sizeof(int)=" << sizeof(int) << "\n";
  std::cout << "sizeof(long)=" << sizeof(long) << "\n";
  std::cout << "sizeof(long long)=" << sizeof(long long) << "\n";
  std::cout << "sizeof(float)=" << sizeof(float) << "\n";
  std::cout << "sizeof(double)=" << sizeof(double) << "\n";
  std::cout << "sizeof(long double)=" << sizeof(long double) << "\n";
}

Expected Output (example on 64-bit): sizeof(bool)=1 sizeof(char)=1 sizeof(int)=4 sizeof(long)=8 sizeof(long long)=8 sizeof(float)=4 sizeof(double)=8 sizeof(long double)=16 (platform dependent)

Limits and literals

#include <iostream>
#include <limits>
int main(){
  std::cout << std::numeric_limits<int>::min() << ".." << std::numeric_limits<int>::max() << "\n";
  int dec = 42;      // decimal
  int hex = 0x2A;    // hexadecimal
  int bin = 0b101010; // C++14 binary literal
  auto big = 1'000'000; // digit separators (C++14)
  std::cout << dec << "," << hex << "," << bin << "," << big << "\n";
}

Expected Output: first line shows int range; second line: 42,42,42,1000000

Character types

#include <iostream>
#include <string>
int main(){
  char c = 'A';
  char32_t uni = U'Ω'; // UTF-32 literal
  std::cout << c << " " << (int)c << "\n";
  std::u32string s(1, uni);
  std::cout << s.size() << "\n"; // prints 1
}

Expected Output: A 65 1

Commonly used keywords (overview)

• Types and storage: auto, const, constexpr, consteval, constinit, mutable
• Flow: if, else, switch, case, for, while, do, break, continue, return
• OOP: class, struct, public, private, protected, virtual, override, final
• Memory: new, delete (prefer RAII/smart pointers)
• Misc: namespace, using, template, typename, this, friend, explicit

Fixed-width types and portability

#include <cstdint>
#include <iostream>
int main(){
  std::int32_t a = 123; // exactly 32-bit
  std::uint64_t b = 456u; // exactly 64-bit unsigned
  std::cout << sizeof(a) << "," << sizeof(b) << "\n";
}

Expected Output (example): 4,8

Signed vs unsigned gotchas

#include <iostream>
int main(){
  unsigned u = 0;
  std::cout << (u - 1) << "\n"; // wrap-around (underflow) on unsigned
}

enum class vs enum

enum class Color { Red, Green, Blue }; // scoped, no implicit to int
// enum { Red, Green, Blue }; // unscoped: names leak into surrounding scope

Modern constants: constexpr, consteval, constinit (overview)

• constexpr: may be evaluated at compile time; usable in constant expressions.
• consteval (C++20): must be evaluated at compile time (immediate function).
• constinit (C++20): ensures a variable is initialized at compile time (not const).

Common Pitfalls

• Assuming sizes are identical across platforms; use sizeof and numeric_limits instead of hardcoding.
• Confusing char as always ASCII; use UTF-aware types/encodings when needed.

Checks for Understanding

1. How do you find the maximum value of an int?
2. What does the single quote in numeric literals do?

Exercises

1. Print sizes of all fundamental integer and floating-point types on your machine.
2. Create variables using decimal, hex, and binary literals that represent the same value and print them.