C Lessons

[Charles Pegge]

I'm taking some time out to study C with a view to making tools for cross platform devlopment. I was surprised to find that GCC works without any switches. I have MinGW installed, and all it needs is:

bin\gcc prog.c

and voila! It compiles to a.exe by default

Here is my crash course so far. C material is very easy to find on the web.


C Source 1

Code: C

1.   int main()
2.   {
3.     return 0;
4.   };
5.  

C Source 2

Code: C

1.   #include <stdio.h>
2.  
3.   int main()
4.   {
5.     // int a;
6.     printf ("Hello World!\n");
7.     return 0;
8.   };

C Source 3

Code: C

1.  
2.   /* malloc example: string generator*/
3.  
4.   #include <stdio.h>
5.   #include <stdlib.h>
6.  
7.   int main ()
8.   {
9.   int i,n;
10.   char * buffer;
11.  
12.   printf ("How long do you want the string? ");
13.   scanf ("%d", &i);
14.  
15.   buffer = (char*) malloc (i+1);
16.   if (buffer==NULL) exit (1);
17.  
18.   for (n=0; n<i; n++)
19.     buffer[n]=rand()%26+'a';
20.   buffer[i]='\0';
21.  
22.   printf ("Random string: %s\n",buffer);
23.   free (buffer);
24.  
25.   return 0;
26.   };
27.  

C Source 4

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/scanf/
2.  
3.   /* scanf example */
4.   #include <stdio.h>
5.  
6.   int main ()
7.   {
8.   char str [80];
9.   int i;
10.  
11.   printf ("Enter your family name: ");
12.   scanf ("%s",str);  
13.   printf ("Enter your age: ");
14.   scanf ("%d",&i);
15.   printf ("Mr. %s , %d years old.\n",str,i);
16.   printf ("Enter a hexadecimal number: ");
17.   scanf ("%x",&i);
18.   printf ("You have entered %#x (%d).\n",i,i);
19.  
20.   return 0;
21.   }
22.  
23.  

C Source 5

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/fopen/
2.  
3.   /* fopen example */
4.   #include <stdio.h>
5.   int main ()
6.   {
7.   FILE * pFile;
8.   pFile = fopen ("myfile.txt","w");
9.   if (pFile!=NULL)
10.   {
11.     fputs ("fopen example",pFile);
12.     fclose (pFile);
13.   }
14.   return 0;
15.  }
16.  

C Source 6

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/setbuf/
2.  
3.   /* setbuf example */
4.   #include <stdio.h>
5.  
6.   int main ()
7.   {
8.   char buffer[BUFSIZ];
9.   FILE *pFile1, *pFile2;
10.  
11.   pFile1=fopen ("myfile.txt","w");
12.   pFile2=fopen ("myfile2.txt","a");
13.  
14.   setbuf ( pFile1 , buffer );
15.   fputs ("This is sent to a buffered stream",pFile1);
16.   fflush (pFile1);
17.  
18.   setbuf ( pFile2 , NULL );
19.   fputs ("This is sent to an unbuffered stream",pFile2);
20.  
21.   fclose (pFile1);
22.   fclose (pFile2);
23.  
24.   return 0;
25.   }
26.  

C Source 7

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/fread/
2.  
3. /* fread example: read a complete file */
4. #include <stdio.h>
5. #include <stdlib.h>
6.  
7. int main () {
8.   FILE * pFile;
9.   long lSize;
10.   char * buffer;
11.   size_t result;
12.  
13.   pFile = fopen ( "myfile.bin" , "rb" );
14.   if (pFile==NULL) {fputs ("File error",stderr); exit (1);}
15.  
16.   // obtain file size:
17.   fseek (pFile , 0 , SEEK_END);
18.   lSize = ftell (pFile);
19.   rewind (pFile);
20.  
21.   // allocate memory to contain the whole file:
22.   buffer = (char*) malloc (sizeof(char)*lSize);
23.   if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}
24.  
25.   // copy the file into the buffer:
26.   result = fread (buffer,1,lSize,pFile);
27.   if (result != lSize) {fputs ("Reading error",stderr); exit (3);}
28.  
29.   /* the whole file is now loaded in the memory buffer. */
30.  
31.   // terminate
32.   fclose (pFile);
33.   free (buffer);
34.   return 0;
35. }
36.  

C Source 8

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/fseek/
2.  
3.   /* fseek example */
4.   #include <stdio.h>
5.  
6.   int main ()
7.   {
8.   FILE * pFile;
9.   pFile = fopen ( "example.txt" , "w" );
10.   fputs ( "This is an apple." , pFile );
11.   fseek ( pFile , 9 , SEEK_SET );
12.   fputs ( " sam" , pFile );
13.   fclose ( pFile );
14.   return 0;
15.   }
16.  

C Source 9

Code: C

1.   // http://www.cplusplus.com/reference/clibrary/cstdio/fgets/
2.  
3. /* fgets example */
4. #include <stdio.h>
5.  
6. int main()
7. {
8.    FILE * pFile;
9.    char mystring [100];
10.  
11.    pFile = fopen ("myfile.txt" , "r");
12.    if (pFile == NULL) perror ("Error opening file");
13.    else {
14.      fgets (mystring , 100 , pFile);
15.      puts (mystring);
16.      fclose (pFile);
17.    }
18.    return 0;
19. }
20.  

Charles

[Peter]

cool Charles,

grandmother's C  is alive !

[efgee]

Charles,
does this:

Code: (o2)

mean that these programs can be compiled with oxygen as well?

[Charles Pegge]

No, it's just a convenient code format. We don't have the standard C libraries but the syntax would be very close.

Charles

[jcfuller]

Charles,
As O2 does classes  might I  suggest that you study up on c++ too (g++) .

James

[Charles Pegge]

Certainly James,

C++ is a closer fit and gcc will do both. (In fact gcc will also do Java, Ada and  Fortran!)

Charles

[Peter]

Hi Charles,

another c-lesson  'DiskFree'

Code: [Select]

#include <windows.h>
#include <stdio.h>

int main(void)
{
 long long BytesAvailable,TotalBytesAvailable=0;
 long long capacity,TotalCapacity=0;
 long long userFree,TotalUserFree=0;
 long long used,TotalUsed=0;
 long double percent;
 int counter = 'C';
 char diskname[512];
 strcpy(diskname,"C:\\");
 printf("%-6s %15s %15s %15s %6s\n","Drive", "Capacity",
 "Available","Used","Free");

 while (counter != (1+'Z'))
 {
  diskname[0] = counter;
  if (GetDiskFreeSpaceEx(diskname, &BytesAvailable,
  &capacity,&userFree))
  {
   percent = 100.0L*(((long double)BytesAvailable)/(long
   double)capacity);
   used = capacity-BytesAvailable;
   printf("%-6s %15'lld %15'lld %15'lld %6.2Lf%%\n",
   diskname,capacity,BytesAvailable,used,percent);
   TotalBytesAvailable+=BytesAvailable;
   TotalCapacity+=capacity;
   TotalUsed+=used;
  }
  counter++;
 }

// Now print the totals
percent = 100.0L*(((long double)TotalBytesAvailable)/(long
double)TotalCapacity);
printf("\n%-6s %15'lld %15'lld %15'lld %6.2Lf%%\n", "Total:",
TotalCapacity,TotalBytesAvailable,TotalUsed,percent);
return 0;
}

[JRS]

What language was used to write the C language?  (ASM, itself, ...)

[Peter]

Hi,

The C programming language was devised in the early 1970s as a system
implementation language for the nascent Unix operating system. Derived
from the typeless language BCPL, it evolved a type structure; created
on a tiny machine as a tool to improve a meager programming
environment, it has become one of the dominant languages of today.

[Charles Pegge]

'C' was developed from 'B' but there was no 'A'.

Interesting how structs arrived so late in the language.

http://en.wikipedia.org/wiki/C_%28programming_language%29

Charles

[Charles Pegge]

Thanks for the DiskFree code Peter.

Function Pointer

Code: C

1.  
2.  
3.   // FUNCTION POINTER
4.  
5.   #include <stdio.h>
6.  
7.   int foo(int i,int j)
8.   {
9.     printf ("Result %i \n",i+j);
10.   }
11.  
12.   int (*pfoo)(int i,int j);
13.  
14.  
15.   int main()
16.   {
17.     pfoo=&foo;
18.     return pfoo(1,2);
19.   }
20.  

Charles

[Peter]

more pointer  

Code: [Select]

#include <stdio.h>

int main()
{
 int i;
 int *p;
 
 i =1;
 p =&i;
 
 printf("\nafter p = &i; is\n");
 printf(" i = %d\n",  i);
 printf(" p = %d\n",  p);
 printf("*p = %d\n", *p);
 
 *p = 2;
 
 printf("\nafter *p = 2; is\n");
 printf(" i = %d\n",  i);
 printf(" p = %d\n",  p);
 printf("*p = %d\n", *p);
 
 printf("\nsizeof(int *) = %d\n", sizeof(int *));
 
 getchar();
 return 0;
}

[Peter]

pointer and malloc

Code: [Select]

#include <stdio.h>
#include <stdlib.h>

int main()
{
 int *p;
 int n =10;
 int i;

 p = (int *) malloc(n * sizeof(int));
 if (!p)
 {
  printf("Error, not enough memory.\n);
  getchar();
  return 0;
 }

 for (i =0; i<10; i++)
  p[i] = 2*i;
 for (i =0; i<10; i++)
  printf("i = %d   p[%d] = %d\n", i, i, p[i]);
 free(p);
 
 getchar();
 return 0;
}



[Peter]

more c- lesson sinus.

Code: [Select]

#include <windows.h>
#include <stdio.h>
#include <math.h>

char text[1000];
int imax, jmax;
const double pi = 3.14159265358979323846;
double frequenz = 1.0;
int n = 100;


void Draw(HDC hdc)
{
  double x, y, dx, xmin, xmax, ymin, ymax;
  double xfaktor, yfaktor;
  int i, j, i0, j0;
 
  xmin = 0;
  xmax = 2*pi*frequenz;
  ymin = -1;
  ymax = +1;
 
  // Intervall
  dx = (xmax - xmin)/n;
 
  // Zoomfaktor
  xfaktor = imax/(xmax-xmin);
  yfaktor = jmax/(ymax-ymin);
 
  // move
  i0 = 0;
  j0 = jmax/2;
 
  MoveToEx(hdc, i0, j0, 0);
  for (x = xmin; x <= xmax + dx/2; x += dx) {
   
    // Funktion
    y = sin(x);
   
    // Pixel
    i = i0 + xfaktor * x;
    j = j0 - yfaktor * y;
   
    // lines/boxes
    LineTo(hdc, i, j);
    Rectangle(hdc, i-2, j-2, i+3, j+3);
  }
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT m, WPARAM wParam, LPARAM lParam)
{
  HDC hdc;
 
  if (m == WM_KEYDOWN) {
    if (wParam == VK_UP    && n < 5000)        n = 3*n/2;
    if (wParam == VK_DOWN  && n > 2)           n = 2*n/3;
    if (wParam == VK_LEFT  && frequenz < 1024) frequenz *= 2;
    if (wParam == VK_RIGHT && frequenz > 0.25) frequenz /= 2;
    InvalidateRect(hwnd, 0, 0);
  }
 
  else if (m == WM_PAINT) {
    hdc = GetDC(hwnd);
    Rectangle(hdc, -1, -1, imax+1, jmax+1);
    Draw(hdc);
    ReleaseDC(hwnd, hdc);
    ValidateRect(hwnd, 0);
    sprintf(text, "Sinus:  f = %.2f  n = %d", frequenz, n);
    SetWindowText(hwnd, text);
  }
 
  else if (m == WM_SIZE) {
    imax = LOWORD(lParam);
    jmax = HIWORD(lParam);
  }
  else if (m == WM_DESTROY)
    PostQuitMessage(0);
  else
    return DefWindowProc(hwnd, m, wParam, lParam);
  return 0;
}



[Peter]

lesson pow/sqrt

Code: [Select]

include "window.h"

Def Lila 0xFFC8C8

Window "Quadratic Color 2011",640,480,ws_overlapped
SetFont 16,32,0,0

single x y ax ay tx ty

While WinExit=0
For x=8 To 16
For y=1 To 420
ax= pow(x,2)
ay= pow(y,2)
tx = sqr(ax+ay)
ty = sqr(ax+ay)
Text "PETER",tx,ty,Rgb (Rand(32,255), Rand(32,255), Rand(32,255))
Next: Next
DoEvents
Wend
WinEnd
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