double and float array type

This is a discussion on double and float array type within the C Programming forums, part of the General Programming Boards category; Hi Guys, So i am using a loop to fill an array from user input. Whats the difference between a ...

  1. #1
    Registered User
    Join Date
    Apr 2008
    Posts
    190

    double and float array type

    Hi Guys,
    So i am using a loop to fill an array from user input.
    Whats the difference between a float and a double because I am not worried:
    Code:
    double init_T[4]={0};
    	for (i = 0; i <= 4; i++)
    	{
    	    //init_T[i] = i+2;
    	    scanf("%f",&init_T[i]);
    	}
    	for (i = 0; i <= 4; i++)
    	{
    	    printf("%f\n",init_T[i]);
    	}
    Input 1 2 3 4 5
    Output
    1
    2
    3
    4
    5
    then change the array to a type double and Output becomes:
    0.00
    0.00
    0.00
    0.00
    0.56556
    Why does the double change everything?

  2. #2
    Registered User
    Join Date
    Jun 2005
    Posts
    6,157
    A double is larger than a float, so needs a different format for scanf() - it is rather critical that scanf() know the actual size of the variable being read. %f is for float. This needs to be modified with a l (letter L) prefix for double (i.e. %lf). The prefix is also need for other floating point formats (%e versus %le, %g versus %lg, etc).

    The l modifier is not required for printf() when printing floating point types (as a float value is implicitly promoted to double when passed by value).

    If you want to work with long double types, then the L format specifier is needed for both scanf() and printf() - %Le, %Lf, %Lg.
    Right 98% of the time, and don't care about the other 3%.

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