OpenMP error invalid controlling predicate [duplicate]

Question

I have written the following code and trying to parallelize it using openmp. but i am unbale to compile the program and end up with error invalid controlling predicate error

#pragma omp parallel for schedule(dynamic, 1)
for( ; i+o<N*C && i < C*n; i++ )
       buf[i] = (a[i]-b[i])*(a[i]-b[i]);

Answer 1

Rewrite the loop like this and it should work:

int maxII = min( N*C-o, C*n);
#pragma omp parallel for schedule(dynamic, 1)
for ( int ii=i; ii<maxII; ii++ )
   buf[ii] = (a[ii]-b[ii])*(a[ii]-b[ii]);

OpenMP for loops have to follow a "Canonical Loop Form" as described in the standard chapter 2.6

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EDIT: "Could you please explain me what was wrong with my code?"

Well, the loop form you used isn't compliant with OpenMP's "Canonical Loop Form" which basically (I over-simply here, sorry) asks that:

• the loop index is clearly defined;
• the lower bound of the loop is given in the initialisation part;
• the test is one of the following operators: <, <=, > or >=; and
• the increment is clear.

I simply rewrote your loop to abide to these simple rules. It was easy enough, as it is in most cases.