wait for threads to finish using pthread_join..?

[wildplace]

bool aCondition = true;

    for(int i=0; i<numOfThreads; i++){

        pthread_create(&firstThreads[i], NULL, &myThreads1, (void*) NULL);
        if(aCondition == true)//for here, if some condition is true i want at least one thread from firstThreads to complete before any secondThreads runs
            pthread_join(firstThreads[0], NULL);    
        pthread_create(&secondThreads[i], NULL, &myThreads2, (void*) NULL);
        }

    for(...)
        //join the rest of the threads
    return;

i have similar structure in my program, but secondThreads seems not waiting firstThreads[0] to finish.