1 #include<iostream> 2 using namespace std; 3 //值传递 4 void sum(int a,int b) 5 { 6     a += 1; 7     b += 1; 8 } 9 //引用传递10 void sum2(int &a,int &b)11 {12     a += 1;13     b += 1;14 }15 //指针传递16 void sum3(int *a,int *b)17 {18     *a += 1;19     *b += 1;20 }21 //默认参数22 void sum4(int a = 4, int b = 5)23 {24     cout<<"a+b= "<<a+b<<endl;25 }26 int main()27 {28     int a = 1, b = 3;29     cout<<"before sum:  a= "<<a<<"\tb= "<<b<<endl;30     //值传递31     sum(a,b);32     cout<<"after sum:  a= "<<a<<"\tb= "<<b<<endl;33     a = 1, b = 3;34     cout<<"before sum2:  a= "<<a<<"\tb= "<<b<<endl;35     //引用传递36     sum2(a,b);37     cout<<"after sum2:  a= "<<a<<"\tb= "<<b<<endl;38     //指针传递39     a = 1, b = 3;40     sum3(&a,&b);41     cout<<"after sum3:  a= "<<a<<"\tb= "<<b<<endl;42     //默认参数43     sum4();44     cin.get();45     return 0;46 }