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There are various contexts where you can use function pointers. For example try the following program

 
 #include <iostream> 
  
 namespace N 
 { 
 void  ( *  for_each( int *first, int *last, void f( int & x ) ) )( int & ) 
 { 
    for ( ; first != last; ++first ) f( *first ); 
  
    return f; 
 } 
 } 
  
 void f1( int &x ) { std::cout << x << ' '; } 
 void f2( int &x ) { if ( x % 2 ) x = -x; } 
  
 int main()  
 { 
 	int a[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }; 
  
 	N::for_each( a, a + sizeof( a ) / sizeof( *a ), f1 ); 
 	std::cout << std::endl; 
  
 	N::for_each( a, a + sizeof( a ) / sizeof( *a ), f2 ); 
  
 	N::for_each( a, a + sizeof( a ) / sizeof( *a ), f1 ); 
 	std::cout << std::endl; 
   
 	return 0; 
 }

The output will be

 
 0 1 2 3 4 5 6 7 8 9  
 0 -1 2 -3 4 -5 6 -7 8 -9

You could introduce a typedef name for the function pointer. In this case the code would look simpler. For example

 
 namespace N 
 { 
  
 typedef void ( *fp )( int & ); 
 fp  for_each( int *first, int *last, fp f ) 
 { 
    for ( ; first != last; ++first ) f( *first ); 
  
    return f; 
 } 
  
 }

You can use for example arrays of function pointers.
You can use also std::function instead of or with function pointers and so on.