method 2 error

void method2()
{
    int i,j;
    struct place *a;
    a=(struct place*)malloc(sizeof(struct place));

    pthread_t threads[rowSize1*colSize2]; /* descriptors of threads */
    for(i = 0; i < rowSize1; i++)  /* create threads */
    {
        for(j=0; j<colSize2; j++)
        {
            a->r=i;
            a->c=j;
            if (pthread_create(&threads[i*j], NULL, executeMethod2, (void *)a))
            {
                printf("Can not create a thread\n");
                exit(1);
            }

        }

    }
    for(i = 0; i < rowSize1; i++)  /* create threads */
    {
        for(j=0; j<colSize2; j++)
        {
            int value; /* value returned by thread */
            pthread_join(threads[i*j], (void **)&value);
            outputMatrix2[i][j]=value;
            printf("%d  ",outputMatrix2[i][j]);
        }
        printf("\n");
    }
}
void *executeMethod2(void *a)
{
    int ans=0;
    struct place *b;
    b=(struct place *)a;
    int n = b->r; /* index of current row in the first matrix*/
    printf("%d current row\n",n);
    int m   =  b->c;/* index of current column in the second matrix*/
        printf("%d current col\n",m);

    int i,j;
    for(i=0; i<colSize1; i++)
    {
        for(j=0; j<rowSize2; j++)
        {
            ans+=matrix1[n][i]*matrix2[j][m];
        }
    }
    /* terminate a thread and return the ans of multiplication */
    pthread_exit((void*)ans);
}