Thread: Very simple Function using printf()

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  1. #1
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    Very simple Function using printf()

    Hello again,

    This code uses a simple function that takes two arguments and just prints them. This is easy when using two int (%d) arguments. However, I want to take two double arguments (i.e. integers with decimal points) but once I start messing with the format specifiers the output goes mental. What am I doing wrong?
    Code:
    #include <stdio.h> 
     
     void printfunc(int, int);
     
     int main(void)
     {
         int dub1, dub2;
         
         printf("Enter two decimal integers.\n");
         scanf("%d %d", &dub1, &dub2);
         printfunc(dub1, dub2);
         printf("Cheerio for now.\n");
         
         getchar();
         getchar();
         
         return 0;
     }
     
     void printfunc(int a, int b)
     {
          printf("%d %d\n", a, b);
          }
    Any guidance most gratefully received.
    To clarify, I need to alter the function to be able to take two double arguments (e.g 1.2 and 56.3) and simply print them, i.e. void printfunc(double, double)

  2. #2
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    I may or may not be right but you have

    scanf("%d %d", &dub1, &dub2);

    remove the & symbols and have it read

    Code:
    scanf("%d %d", dub1, dub2);

  3. #3
    and the hat of int overfl Salem's Avatar
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    > remove the & symbols and have it read
    You need the & in these cases.

    > but once I start messing with the format specifiers the output goes mental. What am I doing wrong?
    Well how many things did you change from 'int' to 'double'?
    And how many formats did you change from %d

    Note that to scanf a double, you need "%lf", but to print it you only need "%f"

    Post an example which doesn't work, if you're still stuck.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  4. #4
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    Quote Originally Posted by Salem View Post
    > remove the & symbols and have it read
    You need the & in these cases.

    > but once I start messing with the format specifiers the output goes mental. What am I doing wrong?
    Well how many things did you change from 'int' to 'double'?
    And how many formats did you change from %d

    Note that to scanf a double, you need "%lf", but to print it you only need "%f"

    Post an example which doesn't work, if you're still stuck.
    Here's my code with the ints changed to doubles and %d changed to %lf (or just %f)

    Code:
    #include <stdio.h> 
     
     void printfunc(double, double);
     
     int main(void)
     {
         int dub1, dub2;
         
         printf("Enter two decimal integers.\n");
         scanf("%lf %lf", &dub1, &dub2);
         printfunc(dub1, dub2);
         printf("Cheerio for now.\n");
         
         getchar();
         getchar();
         
         return 0;
     }
     
     void printfunc(double a, double b)
     {
          printf("%f %f\n", a, b);
          }
    Adding two float values of 1.2 and 2.2 gives a printed output of 1073846681.000000 and -1717986918.000000
    Last edited by twazzler; 04-14-2011 at 12:53 PM. Reason: typo

  5. #5
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    I've just figured it out - I hadn't to changed my ints (dub1 and dub2) to doubles - doh

    Thanks for all your help - I'll be back!

  6. #6
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    Hello twazzler,

    I compiled your latest listing and got this, see if it helps:
    C:\DOCUME~1\Owner>gcc -c test.c -Wall
    test.c: In function 'main':
    test.c:10:6: warning: format '%lf' expects type 'double *', but argument 2 has t
    ype 'int *'
    test.c:10:6: warning: format '%lf' expects type 'double *', but argument 3 has t
    ype 'int *'
    You should always compile with warnings turned on a high level. They catch a lot of stuff.

  7. #7
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    That would have been a big help and saved a lot of time, yes - does Dev-C have such a setting?

    Yes, I know, I should RTFM ;-)

  8. #8
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    I don't know what you are doing but I wrote the following code and it works fine.
    Code:
    #include <stdio.h> 
     
     int main(void)
     {
         double dub1, dub2;
         
         printf("Enter two decimal integers.\n");
         scanf("%lf %lf", &dub1, &dub2);
         printf("\n\n%.2lf\n%.2lf\n\n",dub1, dub2);
         printf("Cheerio for now.\n");
     
         return 0;
     }

  9. #9
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    And how much did twazzler learn about variable types from being handed a fully coded answer?

  10. #10
    Lurking whiteflags's Avatar
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    Well Dev-C++ uses a port of gcc, so look for something that enables -Wall. RTFM.

  11. #11
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    twazzler... you might also consider moving forward in time to a compiler from this millenium... DevC has been abandonware since the late 1990s.

  12. #12
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    Why not using Eclipse?

  13. #13
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    Quote Originally Posted by Mahdiem View Post
    Why not using Eclipse?
    Maybe because it's not C and it appears to be Linux/MAC specific.

    There are lots of free compilers to choose from... Google is your friend.

  14. #14
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    Quote Originally Posted by CommonTater View Post
    twazzler... you might also consider moving forward in time to a compiler from this millenium... DevC has been abandonware since the late 1990s.
    Heh...I'm old skool, chap.

    I'll try your recommendation, can't be any worse than some I have tried (I found Dev-C to be the least annoying and most user-friendly and for some reason it's very hard to get a straight answer from anyone about the "best" IDE to use, especially for beginners).

  15. #15
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    Quote Originally Posted by twazzler View Post
    Heh...I'm old skool, chap.

    I'll try your recommendation, can't be any worse than some I have tried (I found Dev-C to be the least annoying and most user-friendly and for some reason it's very hard to get a straight answer from anyone about the "best" IDE to use, especially for beginners).
    I recommend what CommonTater mentioned. Go for Pelles C. It is easy to install, easy to use and help file is a great deal.

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