// arrfun1.cpp -- functions with an array argument
#include <iostream>
int sum_arr(int arr[], int n); // prototype
const int ArSize = 8;
int main()
{
using namespace std;
int cookies[ArSize] = {1, 2, 4, 8, 16, 32, 64, 128};
// some systmes require preceding int with static to
// enable array initialization
int sum = sum_arr(cookies, ArSize);
cout << "Total cookies eaten: " << sum << endl;
return 0;
}
// return the sum of an integer array
int sum_arr(int arr[], int n)
{
int total = 0;
for (int i = 0; i < n; i++)
total = total + arr[i];
return total;
}編譯輸出： Total cookies eaten: 255 7.3.1 函數(shù)如何使用指針來處理數(shù)組
cookies == &cookies[0] // array name is address of first element
int sum_arr[cookies, ArSize]; ① 根據(jù)C++規(guī)則,，cookies是其第一個元素的地址,，因此函數(shù)傳遞的是地址。 ② 由于數(shù)組的元素的類型為int,，因此cookies的類型必須為int指針,，即int*。 ③ 正確的函數(shù)頭如下： int sum_arr[int * arr, int n] // arr = array name, n = size ④ C++中,，當(dāng)且僅當(dāng),，用于函數(shù)頭或函數(shù)原型中，int * arr 和 int arr[]的含義才是相同的,。它們都意味著arr是一個指針,。 ⑤ 數(shù)組表示法 int arr[] 表明,，arr 不僅指向 int，而且指向 int 數(shù)組的第一個 int,。 ⑤ 當(dāng)指針指向數(shù)組的第一個元素時，使用數(shù)組表示法,；而當(dāng)指針指向一個獨立的值時,，使用指針表示法。 7.3.2 將數(shù)組作為參數(shù)意味著什么
// arrfun2.cpp -- functions with an array argument
#include <iostream>
using namespace std;
int sum_arr(int arr[], int n);
const int ArSize = 8;
int main()
{
int cookies[ArSize] = {1, 2, 4, 8, 16, 32, 64, 128};
cout << cookies << " = array address, ";
cout << sizeof(cookies) << " = sizeof cookies\n";
int sum = sum_arr(cookies, ArSize);
cout << "Total cookies eaten: " << sum << endl;
sum = sum_arr(cookies, 3);
cout << "First three eaters ate " << sum << " cookies.\n";
sum = sum_arr(cookies + 4, 4);
cout << "Last four eaters ate " << sum << " cookies.\n";
return 0;
}
// return the sum of an integer array
int sum_arr(int arr[], int n)
{
int total = 0;
cout << arr << " = arr, ";
cout << sizeof(arr) << " = sizeof arr\n";
for (int i = 0; i < n; i++)
total = total + arr[i];
return total;
}編譯輸出： 0x6ffdf0 = array address, 32 = sizeof cookies 0x6ffdf0 = arr, 8 = sizeof arr Total cookies eaten: 255 0x6ffdf0 = arr, 8 = sizeof arr First three eaters ate 7 cookies. 0x6ffe00 = arr, 8 = sizeof arr Last four eaters ate 240 cookies. ① 首先,，cookies和arr指向同一個地址,。 ② 指針本身并沒有指出數(shù)組的長度，必須顯式傳遞數(shù)組長度,。 ③ &cookies[4]和cookies + 4,；的含義相同，都表示數(shù)組中的第5個元素,。 7.3.3 更多數(shù)組函數(shù)示例
void show_array(const double ar[], int n)
// arrfun3.cpp -- array functions and const
#include <iostream>
const int Max = 5;
// function prototypes
int fill_array(double ar[], int limit);
void show_array(const double ar[], int n); //don't change data
void revalue(double r, double ar[], int n);
int main()
{
using namespace std;
double properties[Max];
int size = fill_array(properties, Max);
show_array(properties, size);
if (size > 0)
{
cout << "Enter revaluation factor: ";
double factor;
while (!(cin >> factor))
{
cin.clear();
while (cin.get() != '\n')
continue;
cout << "Bad input; Please enter a number: ";
}
revalue(factor, properties, size);
show_array(properties, size);
}
cout << "Done.\n";
cin.get();
cin.get();
return 0;
}
int fill_array(double ar[], int limit)
{
using namespace std;
double temp;
int i;
for (i = 0; i < limit; i++)
{
cout << "Enter value #" << (i + 1) << ": ";
cin >> temp;
if (!cin)
{
cin.clear();
while (cin.get() != '\n')
continue;
cout << "Bad input; input process terminated.\n";
break;
}
else if (temp < 0)
break;
else
ar[i] = temp;
}
return i;
}
void show_array(const double ar[], int n)
{
using namespace std;
for (int i = 0; i < n; i++)
{
cout << "Property #" << (i + 1) << ": $";
cout << ar[i] << endl;
}
}
// multiplies each element of ar[] by r
void revalue(double r, double ar[], int n)
{
for (int i = 0; i < n; i++)
ar[i] *= r;
}編譯輸出： // first run Enter value #1: 222000 Enter value #2: 100000 Enter value #3: 300000 Enter value #4: 560000 Enter value #5: 765000 Property #1: $222000 Property #2: $100000 Property #3: $300000 Property #4: $560000 Property #5: $765000 Enter revaluation factor: 0.25 Property #1: $55500 Property #2: $25000 Property #3: $75000 Property #4: $140000 Property #5: $191250 Done. // second run Enter value #1: 45678 Enter value #2: 567890 Enter value #3: 234567 Enter value #4: -2 Property #1: $45678 Property #2: $567890 Property #3: $234567 Enter revaluation factor: 0.56 Property #1: $25579.7 Property #2: $318018 Property #3: $131358 Done. 7.3.4 使用數(shù)組區(qū)間的函數(shù)
double elboud[20]; ① 指針elboud和elboud+20定義了區(qū)間,。數(shù)組elboud指向第一個元素。elboud+19指向最后一個元素,，即elound[19],。因此elboud+20指向數(shù)組結(jié)尾后面的一個位置。 ② 將區(qū)間傳遞給函數(shù)將告訴函數(shù)應(yīng)處理哪些元素,。 // arrfun4.cpp -- functions with an array range
#include <iostream>
int sum_arr(const int * begin, const int * end);
const int ArSize = 8;
int main()
{
using namespace std;
int cookies[ArSize] = {1, 2, 4, 8, 16, 32, 64, 128};
int sum = sum_arr(cookies, cookies + ArSize);
cout << "Total cookies eaten: " << sum << endl;
sum = sum_arr(cookies, cookies + 3);
cout << "First three eaters ate: " << sum << " cookies.\n";
sum = sum_arr(cookies + 4, cookies + 8);
cout << "Last four eaters ate: " << sum << " cookies.\n";
return 0;
}
// return the sum of an integer array
int sum_arr(const int * begin, const int * end)
{
const int * pt;
int total = 0;
for (pt = begin; pt != end; pt++)
total = total + *pt;
return total;
}
Total cookies eaten: 255 First three eaters ate: 7 cookies. Last four eaters ate: 240 cookies. ① 指針cookies + ArSize指向最后一個元素后面的一個位置,。 ② 數(shù)組有ArSize個元素，因此cookies[ArSize-1]是最后一個元素,，其地址為cookies+ArSize-1,。因此，區(qū)間[cookies, cookies+ArSize]指定的是整個數(shù)組,。同樣cookies, cookies+3制定了前3個元素,。 ③ 根據(jù)指針減法原則，end-begin是一個整數(shù)值,，等于數(shù)組的元素數(shù)目,。 ④ 必須按正確的順序傳遞指針。begin在前面,，end在后面,。 7.3.5 指針和const
如果條件允許,，則應(yīng)將指針形參聲明為指向const的指針,。
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