#發問 C語言 Declaration與Definition的困擾

國立臺北科技大學

本人電機系大一，最近在自學C語言，目前閱讀The C Programming Language第二版(K&R2)對於書中變數declaration與definition的敘述感到困惑，由於沒找到程式語言相關版，於是想請教軟體工程師版上的各位前輩一些疑問。如書中p.33所述: "Definition" refers to the place where the variable is created or assigned storage; "declaration" refers to places where the nature of the variable is stated but no storage is allocated. 文中也提到了對於變數的宣告須使用extern關鍵字，但在開頭p.9又提到這樣的例子: A declaration announces the properties of variables; it consists of a name and a list of variables, such as int fahr, celsius; int lower, upper, step; 在我的觀念中，這已不單單是declaration而已，而是declare"並且"define，而往後讀到p.35又發現類似的困惑: Declarations list the variables to be used, and state what type they have and perhaps what their initial values are. 為何declarations又會perhaps state what their initial values are呢? 我希望紮實地學C語言，並搞清楚各類專有名詞的定義，希望有前輩能指點迷津，謝謝。