Create and build a "Hello world" application

Follow these steps to create and build a "Hello world" application:

Create a directory called hello_world:
```
~> mkdir hello_world
```
Inside the hello_world directory, create a file named hello-world.c:
```
~> cd hello_world
~> touch hello-world.c
```

Edit the hello-world.c file with the following contents:

hello-world.c

#include <stdio.h>
#include <unistd.h>
 
int main(int argc, char *argv[]){
    int i;
 
    for (i = 1; i <= 10; i++) {
    printf("%d - Hello world!\n", i);
        sleep(1);
    }
 
    return 0;
}

Create a makefile file inside the hello_world directory:
```
~> touch Makefile
```

Edit the file Makefile with the following contents:

Makefile

BINARY := hello-world
CFLAGS += -Wall -O0
 
.PHONY: all
all: $(BINARY)
 
$(BINARY): hello-world.o
 
.PHONY: clean
clean:
-rm -f *.o $(BINARY)

Before building the code, export the toolchain environment:
```
~> . /opt/dey/2.4-r3/environment-setup-aarch64-dey-linux
```

Cross-compile the code using make.

~> make

If you are building a Qt application, run qmake before cross-compiling:

~> qmake

The binary file, hello-world, is generated inside the directory hello_world.

~> ls -l
total 28
-rwxrwxr-x 1 user user 12084 dic 18 12:39 hello-world
-rw-rw-r-- 1 user user   199 dic 18 12:39 hello-world.c
-rw-rw-r-- 1 user user  4968 dic 18 12:39 hello-world.o
-rw-rw-r-- 1 user user   189 dic 18 12:39 Makefile