C++ Tutorial/Function/function return

More than one returning value

<source lang="cpp">#include <iostream.h> void f (int x, int& prev, int& next) {

 prev = x-1;
 next = x+1;

} int main () {

 int x=100, y, z;
 f (x, y, z);
 cout << "Previous=" << y << ", Next=" << z;
 return 0;

}</source>

Previous=99, Next=101"

Multiple return statements in a function

<source lang="cpp">#include <iostream>

int Doubler(int AmountToDouble);

int main()
{
    int result = 0;
    int input = 123;

    std::cout << "\nBefore doubler is called...";
    std::cout << "\ninput: " << input 
              << " doubled: " << result << "\n";

    result = Doubler(input);

    std::cout << "\nBack from Doubler...";
    std::cout << "\ninput: " << input 
              << " doubled: " << result << "\n\n";

    return 0;
}

int Doubler(int original)
{
    if (original <= 10000)
        return original * 2;
    else
        return -1;
    std::cout << "You can"t get here!\n";
}</source>

Before doubler is called...
input: 123 doubled: 0
Back from Doubler...
input: 123 doubled: 246

Return a double value from a function

<source lang="cpp">#include <iostream> using namespace std;

double box(double length, double width, double height); // use double data

int main() {

 double answer; 

 answer = box(10.1, 11.2, 3.3); // assign return value 
 cout << "The volume is " <<  answer; 

 return 0; 

}

// This version of box uses double data. double box(double length, double width, double height) {

 return length * width * height ; 

}</source>

The volume is 373.296

Return a pointer from a function

<source lang="cpp">#include <iostream> using namespace std;

char *get_substr(char *sub, char *str);

int main() {

 char *substr; 

 substr = get_substr("three", "one two three four"); 

 cout << "substring found: " << substr; 

 return 0; 

}

// Return pointer to substring or null if not found. char *get_substr(char *sub, char *str) {

 int t; 
 char *p, *p2, *start; 

 for(t=0; str[t]; t++) { 
   p = &str[t];
   start = p;  
   p2 = sub;     
   while(*p2 && *p2==*p) { // check for substring 
     p++; 
     p2++; 
   }  

   /* If at end of p2 (i.e., substring), then a match has been found. */ 
   if(!*p2) 
     return start; // return pointer to beginning of substring 
 } 
 return 0;

} /* Quote from: C++: A Beginner"s Guide, Second Edition

1. Publisher: McGraw-Hill Osborne Media; 2 edition (December 3, 2003)
2. Language: English
3. ISBN-10: 0072232153
4. ISBN-13: 978-0072232158

• /</source>

substring found: three four

Return a value from a function

<source lang="cpp">#include <iostream> using namespace std;

int box(int length, int width, int height); // return the volume

int main() {

 int answer; 

 answer = box(10, 11, 3); // assign return value 
 cout << "The volume is " <<  answer; 

 return 0; 

}

// This function returns a value. int box(int length, int width, int height) {

 return length * width * height ; 

}</source>

The volume is 330

Return class instance from a function

<source lang="cpp">#include<iostream.h> class MyClass {

 char ch;

public:

 MyClass(char c)
 {
   ch=c;
      cout << "Constructing";
      cout << ch <<"\n";
 }
 ~MyClass(){
   cout << "Destructing" << ch <<"\n";
 }

}; MyClass createMyClass() {

 MyClass B("B");
 return B;

} main() {

 MyClass A("A");
 createMyClass();
 return 0;

}</source>

ConstructingA
ConstructingB
DestructingB
DestructingA

Returning a reference

<source lang="cpp">#include <iostream>

1. include <string>
2. include <vector>

using namespace std; string& refToElement(vector<string>& inventory, int i); int main() {

   vector<string> inventory;
   inventory.push_back("sword");
   inventory.push_back("armor");
   inventory.push_back("shield");
   cout << refToElement(inventory, 0) << endl;
   //assigns one reference to another -- inexpensive assignment
   string& rStr = refToElement(inventory, 1);
   cout << rStr << endl;
   //copies a string object -- expensive assignment
   string str = refToElement(inventory, 2);
   cout << str << endl;
   //altering the string object through a returned reference
   rStr = "Healing Potion";
   cout << inventory[1] << endl;
   return 0;

} //returns a reference to a string string& refToElement(vector<string>& vec, int i) {

   return vec[i];

}</source>

Returning multiple values from a function using pointer

<source lang="cpp">#include <iostream>

short f(int, int*, int*);

int main()
{
    int number = 2, squared, cubed;
 

    std::cout << "number: " << number << "\n";
    std::cout << "square: " << squared << "\n";
    std::cout << "cubed: "  << cubed   << "\n";
    return 0;
}

short f(int n, int *pSquared, int *pCubed)
{
    *pSquared = n*n;
    *pCubed = n*n*n;
}</source>

number: 2
square: 6
cubed: 2293672

Return void from a function

<source lang="cpp">#include <iostream> using namespace std; void f(); int main() {

 cout << "Before call\n";
 f();
 cout << "After call\n";
 return 0;

} void f(){ cout << "in f\n\n\n"; }</source>

Before call
in f

After call

void function with return statement

<source lang="cpp">#include <iostream> using namespace std;

void power(int base, int exp);

int main() {

 power(10, 2);
 power(10, -2); 

 return 0; 

}

void power(int base, int exp) {

 int i; 

 if(exp < 0) return; /* Can"t do negative exponents. */ 

 i = 1; 

 for( ; exp; exp--) 
    i = base * i; 
 cout << "The answer is: " << i; 
 return;

}</source>

The answer is: 100