主要内容 #
1. 如何读取数组的长度 #
假设有一个很长的数组，如何获得它的长度呢？
int a [] = { 1,4,5,9,15,125,12,12,1,12,14,15,48,787,7,9,9,954,65,32,21,
45,2,9,15,12,1255,12,12,182,9,15,12,125,58,42,9,15,5,12,12,15,12,12,
15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,
12,15,12,12,15,12,12,15,12,12,15,12,12,112,1215,12,12,1,2,9,15,12,1585,
12,12,12,9,152,14,155,12,12,1582,9,15,48,78,0,7,8,9,15,12,9,2,12,9,15,
12,122,125,12,12,1,9,15,12,124,15,48,72,9,15,12,1282,9,15,12,125,12,12,15,12};
换一个问题，小王花了 10 块钱买包子，每个包子 2 元钱，请问他买了几个包子？
类似的，假如我们知道了数组的总大小，也知道数组中一个元素的大小，那么就可以计算出数组中的元素数量了。
在字符串一节中，我们讲解过字符串长度的求法。数组的长度也类似，只不过，数据的末尾没有自动添加的’/0′
请试一试，输出上面数组 a 的大小。
/*
请完成后，查看示例程序
*/
请看代码
#include < iostream >
using namespace std;
int main()
{
int a [] = { 1,4,5,9,15,125,12,12,1,12,14,15,48,787,7,9,9,954,65,32,21,
45,2,9,15,12,1255,12,12,182,9,15,12,125,58,42,9,15,5,12,12,15,12,12,
15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,12,15,12,
12,15,12,12,15,12,12,15,12,12,15,12,12,112,1215,12,12,1,2,9,15,12,1585,
12,12,12,9,152,14,155,12,12,1582,9,15,48,78,0,7,8,9,15,12,9,2,12,9,15,
12,122,125,12,12,1,9,15,12,124,15,48,72,9,15,12,1282,9,15,12,125,12,12,15,12};
int size = sizeof(a) / sizeof(int);
// 注意，sizeof(int) 可以替换为 sizeof(a[0])
cout << "size = " << size << endl;
return 0;
}
2. 遍历数组元素 #
这是一种重要的程序结构，请掌握。
请试一试，使用 while 和 for 遍历下面数组。
int dashima [] = { 1,4,5,9,15,125,12,12,1,12,14,15,48,78,12,12,15,12};
/*
请完成后，查看示例程序
*/
请看代码
#include < iostream >
using namespace std;
int main()
{
int dashima [] = { 1,4,5,9,15,125,12,12,1,12,14,15,48,78,12,12,15,12};
int size = sizeof(a) / sizeof(int);
// while
int i(0);
cout << "Using while: " << endl;
while (i < size)
cout << dashima[i++];
cout << endl << endl;
// for 1
cout << "Using for 1: " << endl;
for (int j = 0; j < size; j++)
cout << dashima[j];
cout << endl << endl;
// for 2
cout << "Using for 2: " << endl;
for (int j = 0; j < size; )
cout << dashima[j++];
cout << endl << endl;
return 0;
}
习题 #
