Question

I was trying to plot a function in GNU plot, and my plot kept differing from the one in the paper. Upon reading that GNU interprets functions as C would, I tried coding the function in C. Same problem.

Eventually I figured out the problem could be exhibited with this tidbit:

#include <stdio.h>
#include <stdlib.h>

int main()
{
double p = 1.0;
double pMinusOneHalf1 = p - (1.0/2.0);
double pMinusOneHalf2 = p - (1/2);

printf("\nFirst = %lf \n Second = %lf\n\n", pMinusOneHalf1, pMinusOneHalf2);

return 0;
}

which gives output

First = 0.500000 
Second = 1.000000

Just wondering if anyone has an explanation as to why C would assume “1” and “2” as INTs inside of the expression for a DOUBLE.

Seems like a very easy thing for people to get caught on. gcc’s -Wall option doesn’t even comment on it.

Answer 1

/ doesn’t particularly care that its result is being subtracted from a double.

All it knows is that it’s given two integers, so it gives you back an integer.