Lecture 2 - Sept 8, 2023

Summary

In this lecture, we discuss computer hardware, input-output using cin and cout, data types and strings. if time permits, we will dig into functions.

Today

Introduction to C++

Assumption

You are familiar with basic C programming (i.e., data types, variables, if statements, loops and functions)

Big picture

Basic computer structure

Structure of a C++ program

Hello world printing in C++

#include <iostream> // standard I/O library in C++
using namespace std; // container for "names"
int main() {
    // cout: output in C++
    // <<: operator to output
    // endl: end of line or new line
    cout << "Hello world!" << endl;
    return 0;
}

Recall in C it was:

#include <studio.h>
int main() {
    printf("Hello world!\n");
    return 0;
}

User enters a value

#include <iostream>
using namespace std;
int main() {
    // cin: input in C++
    // >>: operator to input
    // << value: output a variable
    int value;
    cout << "Enter an integer: " << endl;
    cin >> value;
    cout << "The integer is: " << value << endl;
    return 0;
}

Recall in C it was:

#include <studio.h>
int main() {
    int value;
    printf("Enter an integer: ");
    scanf("%d", &value);
    printf("The integer is: %d\n", value);
    return 0;
}

Data types in C++ and C

These are similar between the two languages.

Integers: 7, 10, 0, -200 (e.g., int attendees 126;)

• int: 32 bits, with range -2^31 to 2^31-1
• short: 16 bits, with range -2^15 to 2^15-1
• long: >= 32 bits

Real numbers: 2.7, -101.25 (e.g. double height = 1.72;)

• float: 32 bits, with 7 digits precision
• double: 64 bits, with 15 digits precision
• long double: >= 64 bits, with 19 digits precision

Characters: a, b, $ (e.g. char firstInitial = 's';)

Logic: true, false (e.g. bool isRaining = false;)

Arrays can be used to store multiple data elements of same type under one variable (e.g. int arr[7] = {1, 2, 3, 4, 5, 6, 7};).

Strings, in C, were null-terminted character arrays (e.g. char h[6] = "hello";). Hello is 5 characters, but we need 6 to store the null character as in hello\0.

In C, you can access the string library functions strcmp, strl;en, strcpy from # include <string.h> (e.g. int x = strlen(str)).

In C++, we have a string “class” that allows you to create a string type variable. You need to include it using #include <string> (e.g. string courseTitle = "Programming Fundamentals";).

You can do interesting operations on strings with

• +: concatenate
• ==: equal to
• !=: not equal to

#include <iostream>
#include <string>

using namespace std;

int main() {
    // == compares strings
    string courseDepart, courseNum, courseCode;
    cout << "Enter the course department and code: " << endl;
    cin >> courseDepart >> courseNum;
    courseCode = courseDepart + courseNum;
    if (courseCode == "ECE244") {
        cout << "That's Programming Fundamentals" << endl;
    }
    return 0;
}

Expressions and statements

These are the same as C

• Arithmetic and relational expressions: x + y, x >= y
• Logical conditions: A || B, A && B, !A
• Decision-making: if and if-else statements
• Repetition: while, do-while, and for loops

Functions

All code must have at least one function (i.e., main function)

Functions allow you to

• Divide code into pieces
• Avoid repetition -> you can reuse code
• Easier to debug

Example: Write a function that gets the factorial of a number

$$n!=n\times (n-1)\times (n-2)\times \cdots 3\times 2\times 1$$

// Function definition
int factorial(int n) {
    int fact = 1;
    for (int i = 1; i <= n; i++) {
        fact *= i;
    }
    return fact;
}

int main() {
    int n = 4;
    // fact: return value stored in fact
    // factorial(n): pass variable
    int fact = factorial(n);
    cout << "Factorial of " << n << " is " << fact << endl;
    return 0;
}

We can’t call a function before it’s declaration. It’s good practice to declare functions first and then define them after the main function.

#include <iostream>

using namespace std;

// Function declaration
int factorial(int n); // or int factorial(int);

// for int factorial(int);
// the first int is the return type
// the second int is the parameter type

int main() {
    int n = 4;
    // fact: return value stored in fact
    // factorial(n): pass variable
    int fact = factorial(n);
    cout << "Factorial of " << n << " is " << fact << endl;
    return 0;
}

// Function definition
int factorial(int n) {
    int fact = 1;
    for (int i = 1; i <= n; i++) {
        fact *= i;
    }
    return fact;
}