C++ Documentation

C++ Basics

Comments

#include <iostream>
using namespace std;

main()
{
    /* comments can be one separate line */
   cout << "Hello World"; // the compiler will ignore this in-line comment
   /* C++ comments can  also
    * take up multiple lines
    * like this one.
    */
   return 0;
}

Comparison Operators

/* Comparison operators return booleans (true/false values) */
/* is x equal to y */
x == y
/* is x not equal to y */
x != y
/* is x greater than y */
x > y
/* is x greater than or equal to y */
x >= y
/* is x less than y */
x < y
/* is x less than or equal to y */
x <= y

Math

/* Remember to include the following line at the top of your program */
#include <cmath>

/* Operators: */
+   Addition
-   Subtraction
*   Multiplication
/   Division
%   Modulus (Remainder)


/* Examples: */
int z = x + y;
int w = x * y;

/* Increment (add one) */
x++

/* Decrement (subtract one) */
x--

/* Absolute value */
double value = double abs(double x)

/* Square Root */
double sqrt = double sqrt(double x)


/* Rounding */
int rounded = round(5.86)


/* Example */
#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    // round
    cout << "round(+3.14) = " << round(3.14)
}
// will print out "round(+3.14) = 3"

Strings

/* To use  strings, you need to import strings, however
  they are included in the iostream import.*/
#include <string>

/* Strings are mutable, so you can change a string
 without rebuilding it. */
 
 string str = "Hello";
 
 // Access and update with [ ] or .at()
 string firstLetter = str[0];
 string secondLetter = str.at(1);
 
 // When updating, replace with a char
 
 str[1] = 'E'; // str is now HEllo
 str.at(4) = 'O'; // str is now HEllO
 
 // Insert adds string to middle of a string
 // str.insert(position, string);

 // Example
 string str = "Word";
 str.insert(3, "l"); // str is now World
 
 /* Substrings are overloaded with two options:
    str.substr(index) Substring from the index to the end
    str.substr(index, length) Substring from the index for 
            a specified length */

 // Examples
 string str = "Hello World";
 
 str.substr(6); // returns "World"
 str.substr(3, 2); // returns "lo"
 
 // Find the length of a string with either
 // length or size
 str.length(); // returns 11
 str.size(); // returns 11
 
 /* The find function returns the first position
  that the search string is found (case sensitive),
  or string::npos if the string is not found. */
  
  str = "Hello World";
  
  str.find("lo"); // returns 3
  str.find("hello") // returns string::npos
  
  if (str.find("hello") != string::npos) {
    cout << "Found" << endl;
  }
  else {
    cout << "Not found" << endl;
  }
 

Function

#include <iostream>
using namespace std;

// function declaration
int min(int num1, int num2);

int main()
{
   // local variable declaration
   int a = 100;
   int b = 200;
   int minimum;

   // calling the min function
   minimum = min(a, b);

   cout << "The minimum value is: " << minimum << endl;

   return 0;
}

// function returning the minimum of two numbers
int min(int num1, int num2)
{
   // local variable declaration
   int result;

   if (num1 < num2) {
      result = num1;
   }
   else {
      result = num2;
   }

   return result;
}

Try/Catch Statements

// Basic Try/Catch Block
try {
    // Block of code to execute that may
    // cause an error
}
catch (error type) {
    // Block of code to execute if the error type
    // is generated
}

// Example: Validating a number
try {
    /* Attempt to convert to a number. If the input
     * is a number, it will work, otherwise it will
     * throw an invalid_argument error.*/
    num = stoi(line);
}
catch (invalid_argument) {
    isValid = false;
    cout << "Not an integer, try again." << endl;
}

Control Structures

If Statement

if (boolean_expression)
{
   // this will execute if the boolean expression is true
}
else
{
  // this will execute if the boolean expression is false
}

// example

#include <iostream>
using namespace std;

int main()
{
   // local variable declaration
   int a = 1;

   // check boolean condition
   if (a < 100)
   {
       // if condition is true then print the next line
       cout << "a is less than 100;" << endl;
   }
   else
   {
       // if condition is false then print the next line
       cout << "a is not less than 100;" << endl;
   }
   cout << "a is equal to: " << a << endl;

   return 0;
}

While Loop

/* while loop syntax */
while (condition) {
   statement(s);
}

/* while loop example */
#include <iostream>
using namespace std;

int main()
{
   int a = 1;

   // while loop execution
   while (a < 100)
   {
       cout << "a is still less than 100! a is: " << a << endl;
       a++;
   }

   return 0;
}

For Loop

/* for loop syntax */
for (initialize; condition; increment) {
   statement(s);
}

/* for loop example */
#include <iostream>
using namespace std;

int main()
{
   // for loop execution
   for (int a = 1; a < 100; a++)
   {
       cout << "value of a: " << a << endl;
   }

   return 0;
}

Input/ Output

Printing

#include <iostream>

using namespace std;

int main()
{
   char str[] = "Hello World!";

   cout << "Programmers love to say : " << str << endl;
}

User Input

There are two main ways to read input from the user. cin is used to read one token at a time. getline is used to read an entire line at a time.

#include <iostream>

using namespace std;

int main()
{
    // To read an entire line, you use the getline command.
    cout << "Please enter a line: ";
    
    // Create a string variable and read in from the user
    string line;
    getline(cin, line);
    
    // To read a single token, you can use the cin command
    cout << "Please enter a token: ";
    string name;
    cin >> name;
    
    return  0;
}

File Input/Output

File input is done by opening a file as an input stream and then reading in using the getline command. Once you capture a line, you can then process it before capturing the next line.

#include <fstream>
#include <iostream>

using namespace std;

int main() {
    
    // Create an input file stream
    ifstream in;

    // Open the file called input.txt
    in.open("input.txt");
    
    // Loop to capture all the line.
    while (true) {
        
        string line;
        // getline reads in our file as a string
        getline(in, line);
        
        /* If you try to read a line and
         * it fails, you know you are at the
         * end of our file and you can break
         * out of the loop */
        if (in.fail()) break;
        
        // process the results
        cout << line << endl;
    }
    // close our input file stream
    in.close();
    return 0;
}

File output is done by opening a file as an output stream and then streaminng into the file just like you would stream to the console.

#include <fstream>
#include <iostream>

using namespace std;

int main() {
    // Create and open the output file
    ofstream out;
    out.open("output.txt");
    
    // Write to the output file
    out << "Hello World!" << endl;
    out << "Nice to meet you" << endl;
    
    // Close the file
    out.close();
    
    return 0;
}

Data Structures

Vectors

#include <vector> // Be sure to include vector
/* syntax to declare a vector */
vector<type> vectorName;

/* declare a vector with intial values */
vector<type> vectorName {value, value, ...};

/* Examples */
vector<string> names;
vector<int> ages {13, 15, 14, 14};

/* Add values to the end of a vector*/
names.push_back("Karel");

/* Use an iterator to add at an index 
   Example: add at index 2 */
 
vector <string>::iterator it = names.begin();
names.insert(it + 2, "Tracy"); 

/* Access the third element of a vector */
double third = weights.at(2);
double third = weights[2];

/* Vector size */
int s = ages.size();

Arrays

/* syntax to declare an array */
type arrayName [ arraySize ];

/* declare a 7-element array called weights */
double weights[7];

/* initialize array */
double weights[5] = {10.0, 200.0, 45.4, 70.0, 99.0};

/* assign 4th elements of the ages array to be 33.0 */
weights[3] = 33.0;

/* index into array to access the third element */
double third = weights[2];

util.h

The util.h file can be imported into any C++ program by using #include "util.h" Below is the header file for the library.

#include <iostream>
#include <vector>

using  namespace std;

// Prints error message and terminates the program
void Error(string message);

// Prints out prompt and returns string line
string readLine(const string prompt = "?");

// Prints out the prompt and returns an integer. If an integer
// is not entered (or it is out of the range), the  reprompt
// is printed and the user can  enter again.
int readInt(const string prompt = "?", string reprompt = "");
int readInt(const int low, const int high, const string prompt = "?", string reprompt = "");

// Prints out the prompt and returns a double. If a double
// is not entered (or it is out of the range), the  reprompt
// is printed and the user can  enter again.
double readDouble(const string prompt = "?", string reprompt = "");
double readDouble(const double low, const double high, const string prompt = "?", string reprompt = "");

// Splits a string based on the delimiter and returns a vector
vector splitLine(string input, char delimeter = ' ');

// Returns uppercasw/lowercase version of a string.
string toUpperCase(string s);
string toLowerCase(string s);

// Random number generator. Returns a random integer.
// Set seed is optional.
void setSeed(int seed);
int randInt();
int randInt(int min, int max);