COMP 322: Introduction to C++
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COMP 322: Introduction to C++
Jan 14, 2022
Lecture 2
(C++ basics)
● Quick recap
● Data types
● Functions
● /* … */ block comment
● // single line comment
● # … preprocessor command
○ #include
content of iostream
● using namespace std
○ Means using namespace std :)
● main() is entry point function
● Operator << to write to cout object
● endl: end line and flush stream
● return 0; to signal that code has
completed successfully
/*
=============================
Name : helloWorld.cpp
Author : Chad
Description : Hello World in C++
=============================
*/
#include
using namespace std;
// main function
int main()
{
cout << "Hello World!" << endl;
return 0;
}
Data Types
● Same as C
○ int : sizeof(int) = 4 (4 at least, on 64-bit system )
○ float : sizeof(float) = 4 (usually 4, which is a 32-bit floating point type)
○ char : sizeof(char) = 1
○ double : sizeof(double) = 8 (which is a 64-bit floating point type)
Sizeof results may vary depending on compiler and operating system (32-bit vs
64-bit)
Data Types
● C++ only
○ string : sizeof(string) = 8 in general on a 64-bit system
○ bool : sizeof(bool) = 1 in general but it is implementation dependent so might
differ from 1
○ auto (since C++11): type automatically deduced from initializer
■ Do not confuse with C auto modifier which is the default for all local
variables
Sizeof results may vary depending on compiler and operating system (32-bit vs
64-bit)
Operator review
● Assignment operator (=)
○ To assign (from right to left) a value to a variable
○ int x = 42;
● Mathematical operators (+, -, *, /, %)
○ Arithmetical operations: add, subtract, multiply, divide, modulo
○ int x = 13%3;
● Relational operators (==, !=, <, <=, >, >=)
○ Test based on comparison
● Logical operators (&&, ||, !)
○ AND, OR, NOT
● Bitwise operators (&, |, ~, ^, <<, >>)
○ AND, OR, NOT, XOR, left shift, right shift
Flow control
● Conditional execution
○ if (condition) … else ...
○ switch (expression) case constant …
● Loops (iterate over the same code multiple times)
○ for (initialization; condition/termination; increment/decrement)
○ for (element:array)
○ while (condition) { … }
○ do { … } while (condition)
Relational or logical operators can be used to evaluate conditions
Flow Control (conditional)
if else switch case
● Expression must be int or char
● Condition is restricted to =
● Case values can be placed in any order
● Can be nested
● Expression can be anything
● Condition can be anything (>, <, =, etc)
● Condition values can be placed in any order
● Can be nested
Flow control
Conditional operator ?: (also called ternary operator because it takes 3 operands)
condition ? expression : expression
max = (x > y) ? x : y;
Equivalent to the following if else statement:
Flow Control (looping)
for while do while
● Executes body at least
once before checking
the condition
● Check condition before
executing the body
● Check condition before
executing the body
Flow Control (looping)
More on for loops
● If x was already initialized, you can:
● Range for loops (since C++11):
int a[] = {0,1,2,3,4,5,6,7,8,9};
for (auto x : a) // for each x in a
cout << x << endl;
Quiz
● What would the following for loop do?
○ for(; ;)
Quiz
● What would the following for loop do?
○ for(; ;)
Infinite loop
Standard input/output
● C++ uses "streams" for reading from (input) and writing to (output) a media
○ Media can be a keyboard, screen, file, printer, etc.
● Input and output streams are provided by the iostream header file
○ #include
● cout stream object is used to print on screen
○ cout << "some message";
○ <<: insertion operator
● Default standard output is the screen
● Similar to printf() in c, system.out.println() in java
Standard input/output
Output:
HelloClass
Output:
HelloClass
Output:
Hello
Class
Standard input/output
Output:
Hello Class
Standard input/output
● cin stream object is used to read from the keyboard
○ cin >> x;
○ >>: extraction operator
● Cin can read strings but limited to one word
○ cin >> stringVariable;
● Use getline function to read a full sentence
○ getline(cin, stringVariable);
● Similar to scanf() in c, scanner class in java
Standard input/output
Namespaces
● A name can represent only one variable within the same scope
● Large projects consists of multiple modules of code provided by different
programmers
○ What happens if one module has a variable name that is the same as another
variable in different module? Name conflict (also called name collision)
● Namespaces solve the name conflict problem
Namespaces
QuebecTemp.h main.cpp
Or also: main.cpp
Functions
● Same as in C and java
● Should be declared before being used
● Declaration should include the name, return type and arguments type
○ Also called prototype or signature of a function
● If the function doesn't return a value, its return type should be declared void
● Functions can be recursive
Recursive Function: example
The factorial function in this example is not
optimal because it is not “tail-recursive”. Can
you rewrite it in a more optimal way?
Factorial is the number of permutations for
a set of objects.
Quiz
● Rewrite the factorial function but in an iterative (non-recursive) fashion.
Quiz
● Rewrite the factorial function but in an iterative (non-recursive) fashion.
Function overloading
● What's the output of the following code?
Function overloading
● What's the output of the following code? (answer is 4 because of implicit
conversion from double to int)
Function overloading
● Multiple functions may have the same name but different number of arguments
○ Int max(int i, int j);
○ Int max(int i, int j, int k);
● Multiple functions may have the same name and same number of arguments but
different types
○ Int max(int i, int j);
○ float max(float i, float j);
● Changing only the return type is not enough
Function overloading
Quiz
● Rewrite the absolute value function from previous example using the ternary
operator ?:
Quiz
● Rewrite the absolute value function from previous example using the ternary
operator ?:
2026-02-25