Find the sum of all the multiples of 3 or 5 below 1000.

This is a discussion on Find the sum of all the multiples of 3 or 5 below 1000. within the C Programming forums, part of the General Programming Boards category; Hi all I have written the following code in C language to 'Find the sum of all the multiples of ...

  1. #1
    Registered User bdeepak23's Avatar
    Join Date
    Nov 2008
    Location
    Bangalore, India
    Posts
    4

    Find the sum of all the multiples of 3 or 5 below 1000.

    Hi all I have written the following code in C language to 'Find the sum of all the multiples of 3 or 5 below 1000' it works fine for i<10 and i<100 and also gives the right answer but for condition i<1000 the answer is in -ve something like -28345. I am trying to understand waht is wrong and how to correct it. (I have a clue of what is wrong :-) but want to hear from the experts here)

    Code:
    //Find the sum of all the multiples of 3 or 5 below 1000.
    #include<stdio.h>
    #include<conio.h>
    void main ()
    {
    int a,b,i,iSum=0;
    	for (i=1;i<1000;i++)
    	{
           a = i%3;
           b = i%5;
    		if(a==0||b==0)
    		{
    			iSum = iSum+i;
    		}
    
    
    	}
    	printf("\nThe sum of all the multiples of 3 or 5 below 1000: %d\n", iSum);
    	getch();
    	clrscr();
    }

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    The sum is larger than 32768, so you need to use an integer type larger than 16 bits.

    You can either use a modern compiler that produces 32-bit code, or change your code to use long int instead of int for the iSum variable.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Registered User slingerland3g's Avatar
    Join Date
    Jan 2008
    Location
    Seattle
    Posts
    602
    At matsp said. You are hitting integer overflow. Also you may consider to use...

    Code:
       iSum += i;

  4. #4
    Registered User bdeepak23's Avatar
    Join Date
    Nov 2008
    Location
    Bangalore, India
    Posts
    4

    Smile Thank you!

    Thanks for the quick response matsp and slingerland. I did have a clue that the value for iSum was overflowing from int but was not very sure.I did change to iSum += i thanks again.

    I tried with TurboC 3.X and TurboC++ 4.5 compilers and GCC 4.2.4 no success yet could you please suggest a decent 32 bit compiler that will run my program? (I am looking for a freeware.)

  5. #5
    Super Moderator
    Join Date
    Sep 2001
    Posts
    4,913
    GCC is very well respected and is considered the de-facto standard. If it's not running your program, you should seriously consider why, and most likely follow the advice. I've used Turbo C 3.0 and 4.5 and really liked them - but they don't follow standard as strictly.

    What kind of error messages are you getting with GCC? One thing that jumps out at me is that you use void main. main should return an int - some compilers allow it, but if I'm not mistaken, gcc doesn't.

    edit: gcc also does not have conio.h - you would use ncurses instead. For simplicity's sake, you might as well just use conio.h on Turbo C.

  6. #6
    Registered User slingerland3g's Avatar
    Join Date
    Jan 2008
    Location
    Seattle
    Posts
    602
    Yeah, that void main() should have knocked me down. If you are entertaining any IDE's I use NetBeans which uses gcc as its compiler.


    http://www.netbeans.org/downloads/

  7. #7
    apprentiCe
    Join Date
    Oct 2008
    Location
    Hyderabad,India
    Posts
    136
    it runs perfectly well in gcc
    Code:
    ............................
    i=957 iSum=213603
    i=960 iSum=214560
    i=963 iSum=215520
    i=965 iSum=216483
    i=966 iSum=217448
    i=969 iSum=218414
    i=970 iSum=219383
    i=972 iSum=220353
    i=975 iSum=221325
    i=978 iSum=222300
    i=980 iSum=223278
    i=981 iSum=224258
    i=984 iSum=225239
    i=985 iSum=226223
    i=987 iSum=227208
    i=990 iSum=228195
    i=993 iSum=229185
    i=995 iSum=230178
    i=996 iSum=231173
    i=999 iSum=232169
    
    The sum of all the multiples of 3 or 5 below 1000: 233168
    i tested

    consider making your datatype to unsigned since you are never interested in dealing with -ve numbers in this scenerio.

    also consider i to be register data-type...as you are using that for iteration, it will be faster.

  8. #8
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    Location
    Canada
    Posts
    8,046
    also consider i to be register data-type...as you are using that for iteration, it will be faster.
    Unless you're actually using a modern compiler that would detect commonly used variables and optimize them into registers automatically.

    Seriously, unless you're doing assembly or embedded programming where you don't have a very good compiler, you probably shouldn't need to use the "register" keyword these days . . . .

    Along with conio.h, getch() and clrscr() are non-standard. Instead of getch(), you can make use of getchar() (see the FAQ). And I really think that you don't need clrscr() . . . but if you really, really want your program to clear the screen after it exits, I suppose you could call system("cls"). That's not much better than clrscr(), though.

    Anyway, about void main: cpwiki.sf.net/void_main
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
    Projects: codeform, xuni, atlantis, nort, etc.

  9. #9
    Registered User whiteflags's Avatar
    Join Date
    Apr 2006
    Location
    United States
    Posts
    7,622
    Quote Originally Posted by creeping death View Post
    it runs perfectly well in gcc
    Code:
    ............................
    i=957 iSum=213603
    i=960 iSum=214560
    i=963 iSum=215520
    i=965 iSum=216483
    i=966 iSum=217448
    i=969 iSum=218414
    i=970 iSum=219383
    i=972 iSum=220353
    i=975 iSum=221325
    i=978 iSum=222300
    i=980 iSum=223278
    i=981 iSum=224258
    i=984 iSum=225239
    i=985 iSum=226223
    i=987 iSum=227208
    i=990 iSum=228195
    i=993 iSum=229185
    i=995 iSum=230178
    i=996 iSum=231173
    i=999 iSum=232169
    
    The sum of all the multiples of 3 or 5 below 1000: 233168
    i tested
    I disagree that it runs perfectly. Why is iSum different from the last line and which total is correct? Your sample output raises more debugging concerns.

  10. #10
    Malum in se abachler's Avatar
    Join Date
    Apr 2007
    Posts
    3,189
    Quote Originally Posted by dwks View Post
    Seriously, unless you're doing assembly or embedded programming where you don't have a very good compiler, you probably shouldn't need to use the "register" keyword these days . . . .
    And in fact doing so may slow your code down.
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

  11. #11
    Dr Dipshi++ mike_g's Avatar
    Join Date
    Oct 2006
    Location
    On me hyperplane
    Posts
    1,218
    I tried using the register keyword several times cos I thought it would make things faster... It always turned out slower than ordinary variables. static variables generally seem to speed things up, but apparently they cripple the optimiser or something. I still use them now and again in functions that get called very often.

  12. #12
    Registered User
    Join Date
    Sep 2008
    Location
    Toronto, Canada
    Posts
    1,831
    Answer is 233168.

    Can also be obtained without loops:
    Code:
    q = 999 / 3;
    sum = (q * q + q) / 2 * 3; // sum of multiples of 3 works out to 166833
    q = 999 / 5; 
    sum += (q * q + q) / 2 * 5; // sum of multiples of 5 works out to 99500
    q = 999 / 15;
    sum -= (q * q + q) / 2 * 15; // sum of multiples of 15 works out to 33165
    ( 166833 + 99500 - 33165 = 233168 )

    </smartass>
    Last edited by nonoob; 03-17-2009 at 05:18 PM.

  13. #13
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    Quote Originally Posted by mike_g View Post
    I tried using the register keyword several times cos I thought it would make things faster... It always turned out slower than ordinary variables. static variables generally seem to speed things up, but apparently they cripple the optimiser or something. I still use them now and again in functions that get called very often.
    Static variables within a function may not be so bad for the optimizer, as they are not truly GLOBAL variables, so the optimizer can know what happens to the variable (as long as the variable is not passed outside in the form of a pointer to or some such).

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  14. #14
    Registered User bdeepak23's Avatar
    Join Date
    Nov 2008
    Location
    Bangalore, India
    Posts
    4
    Hi all,

    Thanks a ton for all the help. I appreciate it! Finally I was able to successfully compile/run this program.

    Turbo C 3.0 and 4.5 int overflow
    Gcc on Ubuntu I think I have not yet installed all the components so it errored out

    I tried Netbeans with cygwin/gcc magically it worked and also gave me the correct results.
    Thank you,
    Deepak

  15. #15
    apprentiCe
    Join Date
    Oct 2008
    Location
    Hyderabad,India
    Posts
    136
    Quote Originally Posted by whiteflags View Post
    I disagree that it runs perfectly. Why is iSum different from the last line and which total is correct? Your sample output raises more debugging concerns.
    oO...what the...i didnt notice that. beats me...i dont see why that should happen...the OP should be more scared than you or I though....

    And in fact doing so may slow your code down.
    hmmm....i dont know

    heres a pretty simple test...

    Code:
    #include<stdio.h>
    
    int main()
    {
        register int i=1;
        while(i>0)
        {
            i++;
        }
        printf("%d",i);
    }
    i measured the time it took ... 3 times
    Code:
    [c_d@localhost C]$ gcc product.c
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.141s
    user	0m8.121s
    sys	0m0.002s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.116s
    user	0m8.108s
    sys	0m0.001s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.121s
    user	0m8.106s
    sys	0m0.000s
    average(register variable)
    realtime=8.126
    usertime=8.111666667
    systime=0.001

    then i changed the program to
    [code]
    Code:
    #include<stdio.h>
    
    int main()
    {
         int i=1;
        while(i>0)
        {
            i++;
        }
        printf("%d",i);
    }
    the time taken were
    Code:
    [c_d@localhost C]$ gcc product.c
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.152s
    user	0m8.126s
    sys	0m0.004s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.167s
    user	0m8.132s
    sys	0m0.001s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.151s
    user	0m8.127s
    sys	0m0.002s
    average:(normal int)
    realtime=8.156666667
    usertime=8.128333333
    systime=0.002333333


    then i modified to
    Code:
    #include<stdio.h>
    
    int main()
    {
        static int i=1;
        while(i>0)
        {
            i++;
        }
        printf("%d",i);
    }
    and the results were
    Code:
    [c_d@localhost C]$ gcc product.c
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.373s
    user	0m8.362s
    sys	0m0.000s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.128s
    user	0m8.122s
    sys	0m0.001s
    [c_d@localhost C]$ time ./a.out
    -2147483648
    real	0m8.690s
    user	0m8.667s
    sys	0m0.003s
    average(static int)
    realtime=8.397
    usertime=8.383666667
    systime=0.001333333


    according to this little experiment...

    performance of register int >int> static int

    I tried using the register keyword several times cos I thought it would make things faster... It always turned out slower than ordinary variables. static variables generally seem to speed things up, but apparently they cripple the optimiser or something. I still use them now and again in functions that get called very often.
    hmm...i heard that static should be used in functions that are called many times, like recursive functions...because...every time , instead of the variables initialising again and again , static would mean one time initialisation, which would save processing time...

Page 1 of 2 12 LastLast
Popular pages Recent additions subscribe to a feed

Similar Threads

  1. a sum equal to or in excess of 100
    By lyoncourt in forum C Programming
    Replies: 6
    Last Post: 10-07-2007, 05:43 PM
  2. ?? with trying to sum numbers
    By Babs21 in forum C Programming
    Replies: 1
    Last Post: 09-16-2007, 03:58 PM
  3. 2Darray in 1Darray and sum elements
    By alzar in forum C Programming
    Replies: 13
    Last Post: 08-29-2007, 02:14 PM
  4. Replies: 3
    Last Post: 06-09-2006, 09:53 AM
  5. Variable question I can't find answer to
    By joelmon in forum C++ Programming
    Replies: 3
    Last Post: 02-12-2002, 03:11 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21