Problem with a mathematical formula

[BianConiglio]

Hi, I'm trying to implement this formula :

http://olimpiadi.ing.unipi.it/oliFor...d23ebfa3f5.gif (the B at the end means that it is expressed in Bytes)

Let say that in my code
length = a
maxLength = k

what's wrong?? I keep having 0.0 and if I debug I don't understand why I'm having 0.0 suddenly after having a positive number in the 2 variables..

#include <stdio.h>

int main (int argc, char *argv[]) {
  int maxLength = 6;
  int length = 21;
  
  double Mb = (((((pow (length, maxLength + 1)) *
		  (length * maxLength - maxLength - 1) + length) /
		 (pow ((length - 1), 2))) / 1024) /1024);
		 
  double Gb = Mb / 1024;
  
  printf("The whole generated traffic will be of %.1f Gb (%.1f Mb).\n\n",Gb,Mb);
  system("PAUSE");  
  return 0;
}

Is it the implementation bugged? Or I've done something stupid? Or both?

thanx

[misplaced]

i think you did something stupid...

try %0.1f before anything else

[Dave_Sinkula]

#include <math.h>

[BianConiglio]

d'ho!!!!!! it was math.h
thanx guys

[misplaced]

.................................................. .........*blink*.................................. ............

how did it compile?.......and what difference would it make (assuming it actually did compile)

[Dave_Sinkula]

how did it compile?.......and what difference would it make (assuming it actually did compile)

Warning W8065 test.c 7: Call to function 'pow' with no prototype in function main
Warning W8065 test.c 9: Call to function 'pow' with no prototype in function main
Warning W8065 test.c 14: Call to function 'system' with no prototype in function main
Warning W8057 test.c 16: Parameter 'argc' is never used in function main
Warning W8057 test.c 16: Parameter 'argv' is never used in function main

Default int return for an unprototyped function.

[BianConiglio]

my devcpp and gcc didnt say a word about that, it was for this that I was confused!

[misplaced]

gcc 3.4.3

C:\temp>gcc err.cpp -o err.exe
err.cpp: In function `int main(int, char**)':
err.cpp:7: error: `pow' undeclared (first use this function)
err.cpp:7: error: (Each undeclared identifier is reported only once for each fun
ction it appears in.)
err.cpp:14: error: `system' undeclared (first use this function)

dev-cpp

g++.exe -c main.cpp -o main.o -I"C:/COMPILERS/BLOODSHED/lib/gcc/mingw32/3.4.2/include"  -I"C:/COMPILERS/BLOODSHED/include/c++/3.4.2/backward"  -I"C:/COMPILERS/BLOODSHED/include/c++/3.4.2/mingw32"  -I"C:/COMPILERS/BLOODSHED/include/c++/3.4.2"  -I"C:/COMPILERS/BLOODSHED/include"   

main.cpp: In function `int main()':
main.cpp:10: error: `pow' undeclared (first use this function)
main.cpp:10: error: (Each undeclared identifier is reported only once for each function it appears in.)
main.cpp:18: error: `system' undeclared (first use this function)

Execution terminated

[BianConiglio]

it looks like u compiled a cpp file, i compiled a c file

[misplaced]

good eye.......

no errors with .c

[BianConiglio]

that's bad, I mean... why the hell should it happen? as far as you guys know, is there a way to extends the controls that the C compiler does?

[misplaced]

sure!

try
gcc file.c -o file.exe -Wall

(-Wall - warn all)

google gcc command line switches

[kryptkat]

works with borland.

C:\borland\bcc55\bin>bcc32 mathform1.c
Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
mathform1.c:
Warning W8065 mathform1.c 17: Call to function 'system' with no prototype in fun
ction main
Warning W8057 mathform1.c 19: Parameter 'argc' is never used in function main
Warning W8057 mathform1.c 19: Parameter 'argv' is never used in function main
Turbo Incremental Link 5.00 Copyright (c) 1997, 2000 Borland

C:\borland\bcc55\bin>mathform1
The whole generated traffic will be of 0.5 Gb (511.0 Mb).

Press any key to continue . . .

C:\borland\bcc55\bin>

/* mathform1.c */

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

int main (int argc, char *argv[]) {
  int maxLength = 6;
  int length = 21;
  
  double Mb = (((((pow (length, maxLength + 1)) *
		  (length * maxLength - maxLength - 1) + length) /
		 (pow ((length - 1), 2))) / 1024) /1024);
		 
  double Gb = Mb / 1024;
  
  printf("The whole generated traffic will be of %.1f Gb (%.1f Mb).\n\n",Gb,Mb);
  system("PAUSE");  
  return 0;
}

you do not need the " (int argc, char *argv[]) "

int main() should work fine.

[misplaced]

(int argc, char *argv[]) is typically automatically created when you create a project in Dev-c++....it's not worth the extra keystrokes to delete it, so most people leave it. i see nothing wrong with it (other than it taking up a few extra byte... oh no)