Introduction

Variables

A variable is an space in memory. To define a variable in C is something like this.:

int weight = 30;
// data_type varioable_name

It is important to say that C is Strongly typed, this means that each variable or constant must have its data type and it cannot change once variable is declared.

Variables in C are mutable by default, so its value could be changed throughout the program

Constants in C are something like this

const double PI = 3.14

A constant is written using UPPER CASE.

Data types

It declares variables and constants. It defines the type and length from associated data in variables.

Data types in C

// Using integers
int

// Using decimals
float // 4 bytes
double // 8 bytes

// Characters
char

// Unsigned
// With this type we'll be able to change data storage
unsigned

Basic Structure

All program in C must have the next structure

• libraries: Always imports the standard library stdio.h
• main method that always has a data type to return

#include <stdio.h>

int main()
{
	printf("Hola mundo"); // This comes from stdio.h
	return 0;
}

Run your first program

To run a C program, first we need to compile it, so we have to run a command to compile it from terminal. In Linux, to do this is using gcc <your-program>.c -o <your-program>

For example

gcc helloWorld.c -o helloWorld
# then you can run t=your program with this

./helloWorld

Print Values

In this case we are using stdio.h to print values in CLI. To index a value we will use something like this: %c:

In C, to define char data types, you must write that inside of ', instead of ":

int main()
{
	char letter = 'A';
	printf("Grettings: %c", letter);
}

Print multiple values

#include <stdio.h>

int main() {
	int a = 0, b = 1;
	printf("In statistics, the probability of something is between %d to %d", a, b);
	return 0;
}

Read Values

To read values is similar to print, we need an indicator to express that we are going to enter a value:

int main()
{
	int entrada_salida;
	printf("Enter your favorite number: ");
	scanf("%d", &entrada_salida);
	
	return 0;
}

Now to print result we add:

int main()
{
	int input_exit;
	printf("Enter your favorite number: ");
	scanf("%d", &entrada_salida);
	printf("Your favorite number is: %d", input_exit);
	
	return 0;
}

Identifiers

Operators

In C programming language exists all operators that exist in other programming language

Arithmetic operators

Each operator follows the sign rules, for example

int main() {
	float a = 10, b = -10;
	// If we rest this, this will converted in a sum
	// If we multiply, this will multiple the signs
	
	float res;
	res = a * b;
	printf("The result is %fl", res);
	// this will be -100
	return 0;
}

Relational operators

Logical operator

Change the datatype of a number

To change the data type, we only need to multiply the number with the datatype that we want to redefine:

For example

int main() {
	int a = 5,b = 2;
	float c;
	// If we divide a / b the result must be 2.5, but both are integers
	c = ((float) a) / b
	printf("%fl\n", c);
	return 0;
}

Also works if we multiply the whole equation for that datatype:

int main() {
	int a = 5,b = 2;
	float c;
	// If we divide a / b the result must be 2.5, but both are integers
	c = (float) a / b
	printf("%fl\n", c);
	return 0;
}