Question

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Why “for( i = 0.1 ; i != 1.0 ; i += 0.1)” doesn’t break at i = 1.0?

I have a numeric (real) interval [x, y]. I must iterate through it using something like:

nr = 0;
for (i = x; i <= y; i += step) //step is a small double value
    nr++;

For [-1, 1] with 0.001 step, it is clear nr should be 2001 (-1.000 … 0.999 1.000), however it computes nr = 2000 (I investigated and it fails the last comparison: 0.999 + 0.001 > 1.000)

How can I compute the exact nr value?

Answer 1

int nsteps = (int)((y-x)/step);
for(int i=0; nsteps; ++i){
   double v = x + (i*step);  // use v in your calculations
}