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;
}

Originally Posted by Emerald

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?).

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".

Originally Posted by Emerald

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".

Originally Posted by Emerald

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.

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