... notes by A.Kamburelis
... will be expanded and translated


Δομές της C (struct = structures)


Δήλωση του νέου τύπου :

struct όνομα { τα πεδία (μέλη) της δομής };


π.χ. complex numbers in C

#include<stdio.h>

struct complex { float Re; float Im; };

main(){
  struct complex z1, z2; // Δήλωση μεταβλητών

  printf("sizeof = %d\n", sizeof(struct complex));

  printf("give z1.Re -> "); scanf( "%f", &z1.Re ); // reading

  z1.Im := 55;

  z2 = z1; // NEW STUFF!

  printf("z2 = %f + i * %f \n", z2.Re, z2.Im );
} 

Note: assigning struct to struct, like z2=z1 above,
assumes that they have same type!


Structs inside structs

eg. color and pixel


#include<stdio.h>

struct color { int r,g,b; };

struct pixel { int x,y; 
  struct color c; // <- struct inside struct
};

main(){
  struct pixel p;
  struct color blue;

  blue.r = blue.g = 0; blue.b = 255; // create blue

  p.x = 12; p.y = 50;

  p.c = blue; // set pixel color to blue

  p.c.r = 50; // correct red of p, but NOT of blue
}



Συναρτήσεις και Δομές


Example:

struct color MyColor ( int Red, int Green, int Blue){
  struct color temp; // prepare temp and return it

  temp.r = Red;
  temp.g = Green;
  temp.b = Blue;

  return temp;
}

using: blue = MyColor(0,0,255);



Returning to our example with complex numbers.


#include<stdio.h>

struct complex { float Re,Im; };


// example: a function that takes structs, and returns a struct

struct complex add ( struct complex a, struct complex b ){
  struct complex help;

  help.Re = a.Re + b.Re;
  help.Im = a.Im + b.Im;

  return help;
}
 

main(){
  struct complex z1, z2, z3;

  z1.Re=z1.Im = 1; // z1=1+i
  z2.Re=z2.Im = 6; // z2=6+6i, so z1+z2=7+7i

  z3=add(z1,z2); // call add

  printf("z3 = %f + i * %f \n", z3.Re, z3.Im );
}



The next remark applies only to C++,
but Visual Studio and DevCpp uses C++ already!

In C++ we have operator overloading!

For example, the + operator can be overloaded, 
to work with our complex numbers.

To do so, write:

struct complex operator+ ( struct complex a, struct complex b )
  struct complex help;

  help.Re = a.Re + b.Re;
  help.Im = a.Im + b.Im;

  return help;
}
 

Now, in main, use just : z3 = z1 + z2; // it works!


You can overload also operators like : -, *, / and %.



Unions (not in lab material).

// Endian example

union trick { int n; unsigned char p[4]; };

void TestEndian (){
  union trick t;

// we want to show the 32 bit number $00 01 02 03
// this value is 1*(256)^2 + 2*256 + 3

  t.n = 1*256*256 + 2*256 + 3;

// print bytes of t.n exactly as they are located in RAM 

  printf("%d %d %d %d\n",t.p[0],t.p[1],t.p[2],t.p[3]);
}

Search for "endianness" in WikiPedia.