c函数默认参数 C++ 函数默认参数

// Using default arguments. 
#include <iostream> 
using namespace std; 

// function prototype that specifies default arguments 
int boxVolume( int length = 1, int width = 1, int height = 1 ); 

int main() 
{ 
    // no arguments--use default values for all dimensions 
    cout << "The default box volume is: " << boxVolume(); 

    // specify length; default width and height 
    cout << "nnThe volume of a box with length 10,n" 
        << "width 1 and height 1 is: " << boxVolume( 10 ); 

    // specify length and width; default height 
    cout << "nnThe volume of a box with length 10,n" 
        << "width 5 and height 1 is: " << boxVolume( 10, 5 ); 

    // specify all arguments 
    cout << "nnThe volume of a box with length 10,n" 
        << "width 5 and height 2 is: " << boxVolume( 10, 5, 2 ) 
        << endl; 
} // end main 

// function boxVolume calculates the volume of a box 
int boxVolume( int length, int width, int height ) 
{ 
    return length * width * height; 
}

#include <iostream>
using namespace std;
const int SIZE = 80;
char * left(const char * str, int n = 1);

int main(){    
    char sample[SIZE];
    cout << "Enter a string:n";
    cin.get(sample,SIZE);
    char *ps = left(sample, 4);
    cout << ps << endl;
    delete [] ps;       // free old string
    ps = left(sample);
    cout << ps << endl;
    delete [] ps;       // free new string
    return 0;
}

char * left(const char * str, int n){
    if(n < 0)
        n = 0;
    char * p = new char[n+1];
    int i;
    for (i = 0; i < n && str[i]; i++)
        p[i] = str[i];  // copy characters
    while (i <= n)
        p[i++] = "0";  // set rest of string to "0"
    return p; 
}