C语言程序设计基础

If For Array

计算机学院    杨已彪

yangyibiao@nju.edu.cn

Review

Variables (变量)   Data Types (数据类型)

Operators (运算符)   Expressions (表达式)

Assignment Statements (赋值语句)

I/O (Input/Output; 输入输出)

Overview

Array (数组)

代码任务

min.c   leap.c   min-array.c

Min

Min of Two

Given two integers $a$ and $b$, to compute their minimum.

$min = \min\{a, b\}$

Min of Two

min = a >= b ? b : a;

(条件表达式; 三目运算符)

Do Not Use it Too Much!

Do Not Be Too Clever!

Min of Three

Given three integers $a$, $b$, and $c$, to compute their minimum.

$\mathit{min} = \min\{a, b, c\}$

Min of a Set of Numbers

Given a set $A$ of integers, to compute their minimum.

$\mathit{min} = \min A$

Leap Year

Leap Year (1): Nested if/else (YES)

Leap Year (2): Nested if/else (NO)

Leap Year (3): else if

Leap Year (4): The Ultimate Version

A year is a leap year if

• it is divisible by $4$ but not by $100$,
• except that years divisible by $400$ are leap years.
  

Short-circuit Evaluation (短路求值)

Min of a Set of Numbers

Given a set $A$ of integers, to compute their minimum.

$\mathit{min} = \min_{i} A_{i}$

$\min\{3, 5, 2, 7\} = \min(\min(\min(3, 5), 2), 7)$

For Statement

Increment/Decrement Operators (++, --)

i = 2;
j = i * i++;

-->

#define NUM 5

Symbolic Constants (符号常量)

int numbers[NUM] = {0}; has a fixed size.

Array Initializer

• int numbers[NUM] = {1};
  
  

• int numbers[] = {0};
  
  

• int numbers[NUM] = {[2] = 1};

Array Initializer (DON’T)

int numbers[NUM] = {};

Forbidden in C99 (Unfortunately!)

Allowed by GCC by default (Unfortunately!!)

Allowed in C23 (Fortunately or not???)

Array Initializer (DON’T)

int numbers[NUM];

numbers may contain garbage values;

always initialize it

Array Initializer (DON’T)

int numbers[];

You must specify the size so that the compiler/runtime can allocate memory for it.

Min of a Set of Input Numbers

Input a set $A$ of $n \ge 1$ integers, to compute their minimum.

$\mathit{min} = \min_{i} A_{i}$