Introduction to C++

Note: All code snippets in this code are shown assuming the readers have used using namespace std in their code.

What is C++?

C++ is a high-level, general-purpose programming language by the Danish Computer Scientist Bjarne Stroustrup, released in 1985 as an extension of C and has undergone various changes over time and is used in various applications such as Game Development, OS Development, Compilers and more.

Structure of a C++ program

The base of a C++ program has the following structure

#include <iostream>
using namespace std;


// driver code 

int main() {

// block of code

return 0
}

Let us understand the code line by line

1. In line 1, we import a library using #include; we are importing the iostream library, which allows us to perform various input/output operations.

2. In line 2, using namespace std allows developers to use identifiers from the standard libraries without needing to prefix them with std::, as a result, we can use cout << instead of std::cout <<

3. In line 4, we see that the method main has a return type int; this is because after the program is executed, the program tells the OS that it has completed/failed its execution. The main is the starting execution point for any C++ program.

4. In line 5, we see we're returning 0; this tells the OS that the program has successfully been executed; if it's any Non-Zero value indicates that the program has failed its execution. If return is not explicitly mentioned, the compiler automatically adds a return 0 by default.

Variables

• int: stores integers (whole numbers), ex: 103, 152312
• double: stores decimal numbers, ex: 12.23, 142.231
• char: stores single characters, such as 'a' or 'b', and must be within single quotes.
• string: stores a sequence of characters as text, such as "This is an example text", and must be within double quotes
• bool: stores only two values: true or false

I/O Operations

In C++, the two standard ways of accepting input and displaying information is as follows:

Input

cin >>

To accept a single variable input, you can do it as

cin >> variable_name

And if you have multiple input data, you can do it as

cin >> variable1 >> variable2 >> variable3

Output

cout <<
To display a single variable, you can do it as follows

cout << variable_name

If you want to display multiple data, you can do it as follows

cout << variable1 << variable2 << variable3

You can end your cout line with endl to move the cursor to the newline to display the following output.

You can format your output in two ways.

1. Using the standard cout

cout << "Value of a is: " << a << " and the value of b is " << b;

1. Using the format library (Available for C++ 20) :

string formatted_string = format("Value of a is: {} and the value of b is {}", a, b);
cout << formatted_string<<endl;

Here, {} acts as placeholders, and the data displayed is mapped to the occurrence of the placeholder and the corresponding variable. In this example, the first placeholder is after :, and the corresponding variable is a, so the value of a will be displayed in the first placeholder, and similarly, the value of b will be displayed in the second placeholder.

Conditional Statements

Conditional Statements are statements that help control the flow of your program based on conditions. There are three types of conditional statements: Simple If , If-Else and If-Else If.

• Simple If In this, if a certain condition is met, a block of code is executed before continuing with the rest of program. This is used when you want to run only a single block of code based on a condition. A Simple If can be written as shown below:

if (condition) {
// your code block here
}

//rest of your code

• If-Else In this, you will have two blocks of code, if a condition is met, the first block of code is executed and the second block of code is ignored before continuing with the rest of the program and if the condition is not met, the first block of code is ignored and the second block of code is executed. The If-Else statement can be written as follows:

if (condition) {
// block 1
} else {
// block 2
}

• If - Else If In this, you will have multiple blocks of code, each to be executed on distinct conditions. It follows the same logic as If-Else but for multiple blocks. The If-Else If statement can be written as follows:

if (condition 1) {
// block 1
} else if(condition 2) {
// block 2
} else if(condition 3) {
// block 3
} else if(condition 4) {
// block 4
} else {
// block 5
}

Loops

A loop allows you to execute a certain block of code as long as a condition is met. There are three types of loops in C++: for loop, do while loop, and while loop.

for loop

This loop allows you to execute a block of code repeatedly as long as a condition is met by using an iterator (a variable that is initialized in the header of the loop), which is checked against a condition and whose value changes in each iteration. A for loop can be written as follows:

for (data_type iterator_name; condition; value_modification) {
    // block of code
}

Here:

• data_type can be int, float, double
• value_modification changes the value of the iterator; you can either increment using iterator_name++ or ++iterator_name, decrement using iterator_name-- or --iterator_name, or perform other operations like multiplication, division, modulus, etc.

while loop

A while loop is an entry-controlled loop; it first checks if the condition is met before running the block of code. As a result, the block of code may not be executed at all if the condition is not met initially.

while (condition) {
    // block of code
}

do while loop

A do while loop is an exit-controlled loop due to its structure. The block of code is first executed and then the condition is checked. As a result, the block of code is guaranteed to execute at least once.

do {
    // block of code
} while (condition);

For each

A For each loop is an iterator through each element in an array or string. In this loop, you access the element directly instead of using the value as an index to access array elements. Here the data type of the iterator depends on the data type of the array, if the array contains only int values, the iterator will be int and if it's a string (C++ 20) or a character array, the iterator will be char. The two ways of using For each is shown below:

• Strings (C++ 20)

string a = "This ai is cool";

for(char c: a){
   cout << c << endl;
}

• Arrays

char a[] = "This ai is cool";

for(char c: a){
   cout << c << endl;
}

Functions

Functions is a block of code that is used to perform a specific operation. Functions are useful when you have blocks of code that can be re-used. A function in C++ can be declared as follows:

RD function_name(optional parameters: data_type variable_name) {
    // block of code

    // return value (if function is not void)
}

Here RD: Return Data Type: A function may or not return a value to the caller of the function, if this is the case, the return data type will be void , else if there is a value to be returned, it can be of the type to be returned, such as char, int, float, double, etc.

int sum(int a, int b) {

    int s = a + b;
    return s;

}