c programming basics

Hello, world in C ( the structure of C program)

#include <stdio.h> 
int main(void)
{
    printf("hello, world\n");
}

In C, the function to print something to the screen is printf, where f stands for “format”, meaning we can format the printed string in different ways. Then, we use parentheses to pass in what we want to print. We have to use double quotes to surround our text so it’s understood as text, and finally, we add a semicolon ; to end this line of code.

To make our program work, we also need another line at the top, a header line #include <stdio.h> that defines the printf function that we want to use. Somewhere there is a file on our computer, stdio.h, that includes the code that allows us to access the printf function, and the #include line tells the computer to include that file with our program.

Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

Types, formats, operators

There are various data types we can use for our variables

bool, a Boolean expression of either true or false
char, a single character like a or 2
double, a floating-point value with even more digits
float, a floating-point value, or real number with a decimal value
int, integers up to a certain size, or number of bits
long, integers with more bits, so they can count higher
string, a string of characters

For printf, too, there are different placeholders for each type:

%c for chars
%f for floats, doubles
%i for ints
%li for longs
%s for strings

And there are some mathematical operators we can use:

+ for addition
- for subtraction
* for multiplication
/ for division
% for remainder

Data Types

In C, we have different types of variables we can use for storing data:

bool 1 byte
char 1 byte
int 4 bytes
float 4 bytes
long 8 bytes
double 8 bytes
string ? bytes

Each of these types takes up a certain number of bytes per variable we create, and the sizes above are what the visual studio, IDE, and most likely your computer uses for each type in C.

Memory

Inside our computers, we have chips called RAM, random-access memory, that stores data for short-term use. We might save a program or file to our hard drive (or SSD) for long-term storage, but when we open it, it gets copied to RAM first. Though RAM is much smaller, and temporary (until the power is turned off), it is much faster.

We can think of bytes, stored in RAM, as though they were in a grid:

Memory

In reality, there are millions or billions of bytes per chip.

In C, when we create a variable of type char, which will be sized one byte, it will physically be stored in one of those boxes in RAM. An integer, with 4 bytes, will take up four of those boxes.
And each of these boxes is labeled with some number, or address, from 0, to 1, to 2, and so on.

c programming basics