03.txt

一個計算機系教授的上課講義 主要是教導學生使用C語言編寫程序

CS 1355
Intro to Programming in C
Monday 2006.9.18 (Week 2)
Lecture Notes (at http://r638-2.cs.nthu.edu.tw/C/notes/03.txt)

Introduction to C Programming (Chapter 2)

Concepts:
- comments
- function declaration
- keywords vs. identifiers
- data types
- expressions
- operators
- variables
- assignments

Comments
- the part of the program text for humans to read 
- start with /* 
  end with   */
  Can be on the same line or span multiple lines
- Example
  /* This program prints "hello world"
     author: Pai Chou, NTHU
     Date: 2006.9.18
   */
- The preprocessor will remove comments before compiling
- Comments are very important!!
  explains things to the human, including yourself in the future

Example program
  /* very simple program */
  #include <stdio.h>
  int main() {
  	printf("hello world\n");
  	return 0;
  }

Function declaration
- What is a function?
  * a mathematical concept:
    - inputs some values, outputs some values
    - examples: (math, not C program statement)
      f(x) = x**2 + 2*x - 3      => this is a quadratic function
      sin(), cos(), tan(), arcsin(), ...  => these are trigonometry functions
    - General "mapping" (癸琈)
      examples:  if P is a person, then you could say
        height(P), weight(P), age(P), name(P), father(P), mother(P), ...
        => in English, say "height of P", "weight of P", "age of P", ...
           just like f(x) is "f of x"
  * a programming concept
    - a piece of program code that can be "called"
      (a "caller" (