Hello,

a working version would look like this:

#include 
#include 
#include 
#include 
#include 
#include 

void MakeRandData(unsigned int* pData, unsigned int nSize)
{

    srand((unsigned int)time(NULL));

    for(unsigned int i =0; i < nSize; i++)
        pData[i] = rand()%(nSize-1);

    unsigned int nMsxPos= rand()%(nSize);
    pData[nMsxPos] = nSize;
    printf("Max value po %d.rn",nMsxPos);
}

int FindMaxIndex(unsigned int* pData, unsigned int nSize)
{
    int nMax = 0, nFindIndex = 0;
    CILK_C_REDUCER_MAX_INDEX(re_nMaxIndex, uint, 0); // max. value with index!
    CILK_C_REGISTER_REDUCER(re_nMaxIndex);

    cilk_for(int i =0; i  < nSize; i++)
    {
        if(pData[i] > REDUCER_VIEW(re_nMaxIndex).value)
        {
            CILK_C_REDUCER_MAX_INDEX_CALC(re_nMaxIndex, i, pData[i]);
        }
    }

    nFindIndex = REDUCER_VIEW(re_nMaxIndex).index;

    CILK_C_UNREGISTER_REDUCER(re_nMaxIndex);
    return nFindIndex;
}

int main(int argc, char* argv[])
{
    const unsigned int MAX_COUNT = 100000000;
    unsigned int* pNData;
    unsigned int nFindMaxPos;

    pNData = new unsigned int [MAX_COUNT];

    MakeRandData(&pNData[0], MAX_COUNT);
    nFindMaxPos = FindMaxIndex(&pNData[0], MAX_COUNT);
    printf("max value posision is %d.rn",nFindMaxPos);

    delete [] pNData;

    return 0;
}

Please note:
i) Reducers need to be registered and unregistered.
ii) CILK_C_REDUCER_MAX_INDEX contains both index & value.
iii) Basic reducer types are already predefined for basic C numeric types (unsigned int for values -> uint as reducer type). See headers (reducer_*.h) for list of all types.
iv) This is not real plain C99 code because of new/delete. Anyways, the exercise was for understanding C reducers if I get it right.

You'll find more information here: http://software.intel.com/en-us/articles/using-an-intel-cilk-plus-reducer-in-c/.

Best regards,

Georg Zitzlsberger