CODEWITHSUNDEEP
c
yasir
yasir

Reputation: 123

Is it possible to convert a non integer number to integer number inside preprocessor directive #define

Is it possible in C language, to convert a non integer number to integer number (closest greater integer) in the pre-processor directive only?

Inside the loop the the Ceil function generally does the job, but I have to define vector(constant size).

#define Lenght_of_box 52.5
#define Vector_size ceil(Lenght_of_box)

Ceil function isn't working inside the pre-processor.

Upvotes: 1

Views: 308

Answers (2)

ryyker
ryyker

Reputation: 23208

..."I need to divide the box into grids of length 1, So for 52.1 or 52.9, I need 53, also negative numbers are not my concern." (from comments)

Given the corner cases you are willing to accept, this macro will work:

#define CEIL(x) (((x)-(int)(x)) > 0 ? (int)((x)+1) : (int)(x))

Tested for the following small sample size:

int main(void)
{
    // float num = 4.0;
    // float num = 4.999;
    float num = 4.001;
    int iNum = CEIL(num);

    printf( "This is a float to int conversion: %d\n", iNum);

    return 0;
}

Upvotes: 3

Bathsheba
Bathsheba

Reputation: 234665

One way is to use

#define f_ 55.1
#define n_ ((int)f_ + !!(f_ - (int)f_))

where n_ is evaluated by the preprocessor, and is f_ rounded up. The !! implements the rounding up.

Test program:

int main()
{
    char n[n_]; // might be a VLA, so runtime `n_` would be permitted ...
    switch (n_){
    case n_: // ...but this will not compile if `n_` is not a constant
        printf("%zu", sizeof(n)); // The value of `n_`
    }
}

Clearly dealing with negative numbers is not a concern.

Upvotes: 6

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