We have used the `stdio.h` file in every program we have used in this course. The file `stdio.h` is a **standard input/output header file**.

In this file, the prototype of the `printf()` function is located, which we also used in all lessons.

**Mistake made to show the example**

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If you disable the `stdio.h` file, the `printf()` function will simply stop working, and when you call this function, we will get an error.

### Header 

Header files such as `std.h` contain declarations of variables, arrays, and function prototypes. This mechanism divides your project code into modules that can be attached as needed. It makes your project more convenient.


### Prototypes
A function prototype is a declaration of a function without its implementation. You can think of a prototype as a "warning" to the compiler that your function exists.
```
type_func name_func(arguments);
```
It looks like a regular function but trimmed. Also, note that this expression ends with a `;`.
What do we do now with our function prototype in a separate header file?


### Multi-file projects
We wrote all our variables and functions in one file, along with the `main` function, but no one does this in professional development. Let's write a function to calculate a capacitor's charge/discharge time depending on the capacitance and resistance.

Our project will have three files:

1. `func.h` - there will be a function prototype;
2. `func.c` - this file will contain the implementation of the function for calculating the charge/discharge time of the capacitor;
3. `main.c` is our main file where all functions will be called.


```
// it's func.h file

#include <stdio.h>

double R, C;

double chrg_dchrg(double R, double C);
```


```
// it's func.c file

#include "func.h"

double chrg_dchrg(double R, double C)
{
	double theta = 5 *((R * C) / 1000);
	return theta;
}
```


```
// it's main.c file

#include "func.h"

int main()
{
    R = 10;
    C = 150;

    printf("Charge/discharge will be %.2f ms\n", chrg_dchrg(R,C));

    return 0;
}
```


After running this program, we get the following:
```
"Charge/discharge will be 7.50 ms"
```
>Note
>
>`%.2f` - `.2` indicates how many decimal places to display.


In this section, the basics of the C-program running will be learned.

This section will teach us how to store data in a computer and create our own data.

This section introduces the fundamental operators that allow us to compare data, assign data, and perform arithmetic operations.

In this section, we will learn about operators that will help us make complex conditions for our programs, which means the actual control of the program.

In this section, you will learn the concept of functions: what they are, what they are used for, and how to create and call them.

In this section, we'll look at pointers, why and when they are used, and briefly touch on the topic of dynamic memory allocation.

C Basics

Header, Prototypes

Header

Prototypes

Multi-file projects

What is the function prototype?