specifier for double type

This is a discussion on specifier for double type within the C Programming forums, part of the General Programming Boards category; Hi, I am new to C programming and also to these boards. I started learning C on my own and ...

  1. #1
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    specifier for double type

    Hi,

    I am new to C programming and also to these boards. I started learning C on my own and I have a small question about the specifier to use for double data types. In the following small code I expected that the last printf statement should display 2.5 but instead i am getting 0.000000. Can someone tell me what I am doing wrong?

    Also when using the float data type is it true that when assigning a value it should include a suffix f the value as otherwise it will be automatically converted to double?

    Thank You

    Code:
    #include <stdio.h>
    int main()
    {
          int number = 0;
          double number2 = 2.5;
          printf("The int variable \"number\" has %d bytes\n", sizeof(number));
          printf("The double variable \"number2\" has %d bytes\n", sizeof(number2));
          (double)number = number2;
          printf("%lf", number);
          system("PAUSE");
          return 0;
    }

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by Emerald View Post
    I am new to C programming and also to these boards. I started learning C on my own and I have a small question about the specifier to use for double data types. In the following small code I expected that the last printf statement should display 2.5 but instead i am getting 0.000000. Can someone tell me what I am doing wrong?
    For printf, use %f to printf doubles (and floats). There is no %lf for printf (only for scanf).

    Also when using the float data type is it true that when assigning a value it should include a suffix f the value as otherwise it will be automatically converted to double?
    If you don't include the "f" suffix, the number is of type double; it's not converted (how can it be, if it was never any other type to begin with?).
    Last edited by Elysia; 08-13-2009 at 07:55 AM.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
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    You can't use casting to change the type of a variable you already declared as something else. Once "number" is an int, it will always be an int. Casting would, however, allow you to cast "number2" to an int and assign that, or you could cast "number" to a double and assign that to "number2".

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    Quote Originally Posted by Emerald View Post
    Hi,

    I am new to C programming and also to these boards. I started learning C on my own and I have a small question about the specifier to use for double data types. In the following small code I expected that the last printf statement should display 2.5 but instead i am getting 0.000000. Can someone tell me what I am doing wrong?
    For scanf, the specifier is "lf". For printf, the specifier is "f".
    Quote Originally Posted by Emerald View Post
    Also when using the float data type is it true that when assigning a value it should include a suffix f the value as otherwise it will be automatically converted to double?
    Literal values that appear in your code (such as 7.5 or 3.4) are doubles unless you tack an f on them (or unless they don't have a decimal point, like 6, in which case they are int). The conversion from double to float usually doesn't cause any problem.

  5. #5
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    Thank you all for the replies, it makes much more sense now.

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