Variables types

Lesson

Try running the following code in python:

a = "Hello "
b = 3
print(a + b)

It will show an error.

The reason is, something called types exists.
In the memory, types are treated differently and they possess different operations.
It makes sense that we can’t add a string and a number.\

In Python, types are mostly implicit.
However, in other languages, they are explicit.
That way, the programmer knows what type of data a variable contains.

C++:

#include <iostream>
#include <string>

int main()
{
    std::string myStringValue = "Hello "; // multiple characters
    int myIntegerValue = -3; // an integer, that can be negative or positive
    bool myBooleanValue = false; // a boolean, being either true or false
    float myFloatingPointValue = 4.3f; // a decimal number, negative or positive 
    char myCharacterValue = 'o'; // a character from the ascii table 
}

As you saw, std::string is a bit special.
It is because strings aren’t a native type.
They do not even exist as “strings” in C: they are treated as a list of characters.
Lists will be discussed in a future chapter.

Types are only written when the variable is first declared.

#include <iostream>

int main()
{
    int i;
    i = 5;
    std::cout << i << std::endl;
}

Sometimes, we might want to convert a type into another type.
Some convertions can be implicit, but the preferred way is doing it explicitly.

#include <iostream>

int main()
{
    float a = 5.983f;
    int b = (int) a; // explicit conversion to an integer
    std::cout << b << std::endl;
}

In that case, the decimal part will be lost and the program will print 5.

Printing in C is also complex, because it depends on the type.\

#include <cstdio>

int main()
{
    int number = 3;
    printf("Number : %d", number);
}

%d for digits (integers), %s for strings, %c for characters, among others.