You will learn:
- keyword
static - Operators:
& * (unary) - How to create and initialize arrays
- Pointers
- Writing Functions that process arrays
- Two-dimensional arrays
An array is composed of a series of elements of one data type.
记住数组最大的特点：在内存中连续存放，有顺序。
Declare arrays
Float candy[365]; char code[12]; int states[50]
- 数组从0开始计数，用 candy[0] 表示第 1 个元素， candy[364] 表示第 365 个元素。
int powers[8] = {1, 2, 3, 4, 5, 6, 7, 8};
...
Listing 10.1 presents a short program that prints the number of days per month
#include#define MONTHS 12 int main() { int days[MONTHS] = {31, 28, 31, 30, 31,30, 31,31, 30, 31, 30, 31 }; int index; for (index = 0; index < MONTHS; index++) printf("Month %d has %2d days.n", index + 1, days[index]); return 0; }
Output
➜ C10_ArraysAndPointers ./a.out Month 1 has 31 days. Month 2 has 28 days. Month 3 has 31 days. Month 4 has 30 days. Month 5 has 31 days. Month 6 has 30 days. Month 7 has 31 days. Month 8 has 31 days. Month 9 has 30 days. Month 10 has 31 days. Month 11 has 30 days. Month 12 has 31 days.
Using const with Arrays
const int days[MONTHS] = {31, 28, 31, 30, 31,30, 31,31, 30, 31, 30, 31 };
Now it is a read-only array.
定义数组的时候要初始化，否则数组可能为任何值，及原本处于对应数组内存位置的值。
定义数组时可以不指定元素个数，由编译器自动计算
const int days[] = {31, 28, 31, 30, 31,30, 31,31, 30, 31, 30, 31 };
在这种情况下，可以在 for 循环中用 sizeof <数组名> / sizeof <数组名[0]> 计算数组元素个数:
for (index = 0; index < sizeof days / sizeof days[0]; index++) ...Designated Initializers (C99)
C99 added a new capability: designated initializers. This feature allows you to pick and choose which elements are initialized.
简单来说，就是你可以挑选数组中的任意值进行初始化。并且其它没有初始化的元素将被自动设为默认值（如 0，空字符等）
下面两条语句等价：
int arr[6] = {0, 0, 0, 0, 0, 212};
int arr[6] = {[5] = 212};
Listing 10.5
#include#define MONTHS 12 int main() { int days[MONTHS] = {31, 28, [4] = 31,30,31,[1] = 29 }; int index; for (index = 0; index < MONTHS; index++) printf("Month %d has %2d days.n", index + 1, days[index]); return 0; }
Output
➜ C10_ArraysAndPointers ./a.out Month 1 has 31 days. Month 2 has 29 days. Month 3 has 0 days. Month 4 has 0 days. Month 5 has 31 days. Month 6 has 30 days. Month 7 has 31 days. Month 8 has 0 days. Month 9 has 0 days. Month 10 has 0 days. Month 11 has 0 days. Month 12 has 0 days.
以上程序看出
- 当初始化第五个元素后，后面默认初始化后面的元素，除非指定第几个元素。
- 如果某个元素初始化了多次，则最后一次的初始化生效（编译器会提警告）。
After an array has been declared, you can assign values to array members by using an array index.
数组可以通过使用索引赋值。
... a[2] = 3; ...
数组名的值即为数组第一个元素的地址。
#include#define SIZE 5 int main() { int envs[SIZE] = {1, 2,3, 4, 5}; int i; printf("The value of envs is %pn", envs); for (i = 0; i < SIZE; i++){ printf("%p >>> %dn", &envs[i], envs[i]); } return 0; }
Output
➜ C10_ArraysAndPointers ./a.out The value of envs is 0x16bc73610 0x16bc73610 >>> 1 0x16bc73614 >>> 2 0x16bc73618 >>> 3 0x16bc7361c >>> 4 0x16bc73620 >>> 5
数组只有在初始化时候可以整体赋值。初始化以后，只能对各个元素单独操作
下面的程序展示了几种数组的错误操作方式：
#includeArray Bounds#define SIZE 5 int main(void) { int oxen[SIZE] = {5, 3, 2, 8}; int yaks[SIZE]; yaks = oxen; // not allowed yaks[SIZE] = oxen[SIZE]; // out of range yaks[SIZE] = {5, 3, 2, 8}; // doesn't work return 0; }
C语言编译器不检查数组越界！！！
#include#define SIZE 5 int main(void) { int oxen[SIZE] = {5, 3, 2, 8}; for(int i = 0; i < SIZE + 2; i++) { printf("%d >>> %dn", i, oxen[i]); } return 0; }
Output
➜ C10_ArraysAndPointers ./a.out 0 >>> 5 1 >>> 3 2 >>> 2 3 >>> 8 4 >>> 0 5 >>> 1 // out of range 6 >>> -374800268 // out of range
C trusts the programmer to do the coding correctly and rewards the programmer with a faster program.
下面的程序逆向输出斐波那契数列
#include#define SIZE 10 int main(void) { int feibo[SIZE] = {1, 1}; for(int i = 2; i < SIZE; i++) { feibo[i] = feibo[i-1] + feibo[i-2]; } for(int i = 0; i < SIZE; i++) { printf("feibo %d >>>>> %dn", i+1, feibo[i]); } int i = 0; int j = sizeof feibo / sizeof feibo[0] - 1; int tmp; while (i < j) { tmp = feibo[i]; feibo[i] = feibo[j]; feibo[j] = tmp; i++; j--; } printf("inverse the feibo sequence...n"); for(int i = 0; i < SIZE; i++) { printf("feibo %d >>>>> %dn", i+1, feibo[i]); } return 0; }
Output
➜ C10_ArraysAndPointers ./a.out feibo 1 >>>>> 1 feibo 2 >>>>> 1 feibo 3 >>>>> 2 feibo 4 >>>>> 3 feibo 5 >>>>> 5 feibo 6 >>>>> 8 feibo 7 >>>>> 13 feibo 8 >>>>> 21 feibo 9 >>>>> 34 feibo 10 >>>>> 55 inverse the feibo sequence... feibo 1 >>>>> 55 feibo 2 >>>>> 34 feibo 3 >>>>> 21 feibo 4 >>>>> 13 feibo 5 >>>>> 8 feibo 6 >>>>> 5 feibo 7 >>>>> 3 feibo 8 >>>>> 2 feibo 9 >>>>> 1 feibo 10 >>>>> 1
C99 中不允许使用变长数组。
C11可以使用变长数组。
如
int n = 10; float arr[n]; // not allowed before C99.
