[C++] 用Xcode來寫C++程式[4] 函數

標籤：

用Xcode來寫C++程式[4] 函數

 

 

此節包括引用函數,內嵌函式,防止修改函數入參,函數自身帶有預設值.

引用函數:防止複製對象,減少系統開銷

內嵌函式:編譯的時候根據具體情形將代碼嵌入進去,成不成功編譯器說了算,減少系統開銷提升效能

引用函數(防止篡改初始值的入參聲明方式):防止修改資料來源

函數參數帶有預設值:函數的某個參數可以給定預設值,精簡函數的使用

 

最簡單的函數

#include <iostream>using namespace std;int addition (int a, int b) {    return a + b;}int main () {    int z;    z = addition (5,3);    cout << "The result is " << z << endl;}

列印結果

The result is 8Program ended with exit code: 0

 

 

 

傳遞引用(int& 表示)

#include <iostream>using namespace std;void duplicate (int& a, int& b, int& c) {    a *= 2;    b *= 2;    c *= 2;}int main () {    int x = 1, y = 3, z = 7;    duplicate (x, y, z);    cout << "x=" << x << ", y=" << y << ", z=" << z << endl;        return 0;}

列印結果

x=2, y=6, z=14Program ended with exit code: 0

 

 

 

防止篡改資料來源(const 修飾變數)

#include <iostream>#include <string>using namespace std;string concatenate (const string& a, const string& b) {    return a + b;}int main () {        string x = "You";    string y = "XianMing";    cout << concatenate(x, y) << endl;        return 0;}

列印結果

YouXianMingProgram ended with exit code: 0

 

 

 

內嵌函式(減少函數調用開銷)

#include <iostream>#include <string>using namespace std;inline string concatenate (const string& a, const string& b) {    return a + b;}int main () {        string x = "You";    string y = "XianMing";    cout << concatenate(x, y) << endl;        return 0;}

列印結果

YouXianMingProgram ended with exit code: 0

 

 

 

帶預設值的函數(如果不賦值,則有一個預設值)

#include <iostream>using namespace std;int divide (int a, int b = 2) {    int r;    r = a / b;    return (r);}int main () {    cout << divide (12)    << endl;    cout << divide (20, 4) << endl;        return 0;}

列印結果

YouXianMingProgram ended with exit code: 0

 

 

 

函數先聲明,後使用

#include <iostream>using namespace std;void odd (int x);void even (int x);int main() {    int i;    do {        cout << "Please, enter number (0 to exit): ";        cin >> i;        odd (i);    } while (i!=0);        return 0;}void odd (int x){    if ((x%2)!=0) cout << "It is odd.\n";    else even (x);}void even (int x){    if ((x%2)==0) cout << "It is even.\n";    else odd (x);}

 

 

 

遞迴調用

#include <iostream>using namespace std;long factorial (long a) {    if (a > 1)        return (a * factorial (a-1));    else        return 1;}int main () {    long number = 9;    cout << number << "! = " << factorial (number);    return 0;}

列印結果

9! = 362880Program ended with exit code: 0

 

[C++] 用Xcode來寫C++程式[4] 函數