C++ Tutorial/Function/function prototype

Returning a pointer from function

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

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

using namespace std; string* ptrToElement(vector<string>* const pVec, int i); int main() {

   vector<string> i;
   i.push_back("A");
   i.push_back("B");
   i.push_back("C");
   cout << *(ptrToElement(&i, 0)) << "\n\n";
   string* pStr = ptrToElement(&i, 1);
   cout << *pStr << "\n\n";
   string str = *(ptrToElement(&i, 2));
   cout << str << "\n\n";
   *pStr = "test";
   cout << i[1] << endl;
   return 0;

} string* ptrToElement(vector<string>* const pVec, int i) {

   return &((*pVec)[i]);

}</source>

Use a function prototype to enforce strong type checking

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

1. include <cstdlib>

using namespace std;

void f(int i); // prototype

int main() {

 int x = 10;   
 f(x);

 return 0; 

}

void f(int i) {

 i = i * i;  
 cout << i;

}</source>

100

Use a function"s definition as its prototype, appears before main

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

bool isEven(int num) {

 if(!(num )) 
     return true; 
 return false;  

}

int main() {

 if(isEven(4)) 
     cout << "4 is even\n";  
 if(isEven(3)) 
     cout << "this won"t display";  
 
 return 0;  

}</source>

4 is even