realloc/calloc
切記切記,兩個的 parameter 不太一樣,我老是忘記,然後就 Segmenation fault
word_freq = (char*)calloc(i , sizeof(char));
word_freq = (char*)realloc(word_freq,i * sizeof (char));
word_freq = (char*)realloc(word_freq,i * sizeof (char));
切記切記,兩個的 parameter 不太一樣,我老是忘記,然後就 Segmenation fault