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Week 2 (August 29, 31): Fundamental Data Types, Variables, Strings

This week we will be going over the following topics:

  • Variables (what they are, how to declare/define, how to assign a new value, rules for variables)
  • C++ data types (numerical and character)
  • Using pre-defined libraries
  • Using character and string data types
  • string class member functions

Monday August 29, 2022:

Wednesday August 31, 2022:

  • Week 2.3 Characters & Strings.pdf 

    https://csusb.instructure.com/courses/14455/pages/week-2-august-29-31-fundamental-data-types-variables-strings?module_item_id=1115396# - char_examples.cpp - https://csusb.instructure.com/courses/14455/files/2446205/download?download_frd=1 - Weeks 2-4 Course Schedule.docx

    https://csusb.instructure.com/courses/14455/pages/week-2-august-29-31-fundamental-data-types-variables-strings?module_item_id=1115396#

Notes

Data types of char values

Characters

values that represent one single character |C++ Keyword|Size|range of values| |-|-|-| |char|1 byte|0 to 127| - Note: uses ASCII

Character Variables

use char to represent data that only requires a single character - chat input; - char marital_status; char variable values must be within apostrophes and can only be a single character - char s = 115; //ok - char s = 'S'; //ok - char x = 'XX'; //not ok

convert variable to Ascii character value

(char)variableName

Strings

  • values that represent a secuqnce of characters
  • this is a complex data type meaning it is made up of another data type (characters)
  • the string class allows us to use string objects
    • #include string |C++ Keyword|Size|range of values| |-|-|-| |string|# of characters * 1 byte|depends on hardware|
  • use strings when you need to represent one or more characters
  • if you use strings, make sure you have #include <string>
  • string variable values must be within quotation marks.
  • each character allocates its own space in memory (1 byte) and has a position number associated with it
    • position numbers start at 0! not 1!

example

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string name = "Sally";
    cout << "Your name is " << name << "\n";

    //change string value
    name = "Bob"; //replaces value in memory
    cout << "Your name is " << name << "\n";

    return 0;
}

Output:

Your name is Sally
Your name is Bob
  • We can store values into strings with cin
    • cout << "Enter your first name:";
    • cin >> name; //user enters Bob
    • cout << name
getline()

if we want to store the entire input, we can use the getline() function getline (istream is, string str) - first argument is the input stream to extract characters from (we use cin) - second argument is the string to store the extracted characters - getline() extracts all characters from is and stores them into str until the newline - if there is a value stored in str, it will be overwritten

string fullName;
cout << "Enter your full name: ";
getline (cin, fullName);
cout << "Your name is: " << fullName;

String member functions

  • #include <string> gives us access to string member fucntions that allow us to manipulate strings and access information about them
  • syntax to use string member functions:
    • stringName.functionName(parameters)

.length()/.size() - length

.length()/.size(): invoked with a string and no parameters but it returns the number of characters in the string (int)

string fullName = "Bob Ross";
int n = fullName.length(); // n = 8
int x = fullName.size(); // x = 8
  • note that the space is its own character

each string character has a position # the last position # is always equal to stringName.length()-1

fullName |B|o|b| |R|o|s|s| |-|-|-|-|-|-|-|-| |0|1|2|3|4|5|6|7|

.substr() - substring

The .substr() function can be called in two different ways .substr(i,n): returns the substring where i is the starting position # and then extracts n characters

string fruit = "watermelon";
string h2o = fruit.substr(0,5);
cout << h2o << "\n"; // will display "water"
string idea = fruit.substr(2,4);
cout << idea << "\n"; // will display "term"

.substr(i): returns the substring where i is the starting position #, to the end of the strin

string richMan = fruit.substr(6)
cout << richMan << "\n"; // will display "elon"
.at(i) - character in string

.at(i): returns the character at position #i

string fruit = "watermelon";
int mid = fruit.length() / 2; //mid = 5
cout << "The middle character in \"' << fruit << "\" is \"" << fruit.at(mid) << "\"\n";

Output: 

The middle character in "watermelon" is "m"
String Concatenation
  • We can put string values together "+"
string fname = "Bob";
string lname = "Ross";
string name = fname + " " + lname;