Making code parallel isnt always the solution, because it also makes overhead for that. Your primary task should be finding the slow parts of code and redesign them.
As I see you often writing in the writeToAnswerFile file. That looks like a bottleneck. I would try to store that information in a string and write if needed
once if all is done.
for (int operation = 0; operation < numberOfOperator;operation++) {
tempOperationSequence[operation] = operationSequence[operation];
}
I would replace
memcpy(tempOperationSequence, operationSequence, operation);
on different places in your code.
The only thing for parallel is the sorting. Google for further information.