//
//  fun with reference parameters
//
 
#include <iostream>
 
// a normal function
int foo1(int x) {
    return x*4;
}
 
// an unsuccessful attempt to return a value through a parameter
void foo2(int x) {
    x = x*4;
}
 
// reference parameters allow us to change the value of something
// passed to us. But the "normal function" approach is preferred.
void foo3(int &x) {
    x = x*4;
}
 
// We can use reference parameters to get more than one value back
// to the caller. There are other ways to solve this problem, but
// this approach is use. Probably not great if you are trying to
// get 23 values back. More on that latter.
void return_more_than_one_thing(int in1, int in2, int &out1, int &out2) {
    out1 = in1 - in2;
    out2 = in2 - in1;
}
 
// a tempting problem to use references for
void swap(int &one_place, int &another_place) {
    int temp;
    temp = one_place;
    one_place = another_place;
    another_place = temp;
}
 
// another use of references is to return values and to use
// the return only for returning the status of the operation.
int divide(double dividend, double divisor, double &quotient) {
    if (divisor == 0){
        return 0;
    }
    quotient = dividend/divisor;
    return 1;
}
 
using namespace std;
 
int main() {
    cout << "trying function foo1 " << foo1(42) << endl << endl;
 
    int x = 42;
    cout << "x before function foo2 " << x << endl;
    foo2(x);
    cout << "x after function foo2 " << x << endl <<endl;
 
    cout << "x before function foo3 " << x << endl;
    foo3(x);
    cout << "x after function foo3 " << x << endl <<endl;
 
    // this will not work:
    // foo3(14);
 
    int y = 12;
    int normal_difference = 98;
    int reverse_difference = 99;
    cout << "Before function return_more_than_one_thing " << x << " " << y << " " << normal_difference << " " << reverse_difference << endl;
    return_more_than_one_thing(y, 14, normal_difference, reverse_difference);
    cout << "After function return_more_than_one_thing " << x << " " << y << " " << normal_difference << " " << reverse_difference << endl << endl;
 
    cout << "Before function swap " << x << " " << y <<  endl;
    swap(x, y);
    cout << "After function swap " << x << " " << y << endl << endl;
 
    // safe division
    double quotient = 31.6;
    cout << "Trying to divide 23 by 45\n";
    if (divide(23,45,quotient)) {
        cout << "All is well, division operation is valid and yields: "  << quotient << endl;
    }
    else {
        cout << "You can not divide by 0, no valid quotient.\n";
    }
    cout << endl;
 
    cout << "Trying to divide 23 by 0\n";
    if (divide(23,0,quotient)) {
        cout << "All is well, division operation is valid and yields: "  << quotient << endl;
    }
    else {
        cout << "You can not divide by 0, no valid quotient.\n";
    }
 
 
 
 
    char ch;
    cin >> ch;
    return 0;
}
cs-142/reference-parameters.txt · Last modified: 2015/10/13 20:31 by kseppi
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