This chapter is from the book
This chapter is from the book
This chapter is from the book
This chapter is from the book
Using Recursion
Functions can call themselves in Objective-C, a process called recursion, and this process is often useful. For example, say you’re writing a function that calculates factorials: for example, 6! =6 x 5 x 4 x 3 x 2 x 1 = 720. Here’s a function that calls itself recursively to figure out factorials:
int factorial(int value)
{
if (value == 1) {
return value;
} else {
return value * factorial(value - 1);
}
}
Let’s use this function to calculate 6!.
To use recursion:
- Create a new program named functionrecursion.m.
- In functionrecursion.m, enter the code shown in Listing 4.17.
This code calls the factorial() function, passing it a value of 6.
- Add the code to implement the recursive factorial() function (Listing 4.18).
- Save functionrecursion.m.
- Run the functionrecursion.m program.
You should see the following:
6! = 720
Listing 4.17. Starting functionrecursion.m.
#include <stdio.h>
int main()
{
printf("6! = %i\n", factorial(6));
return 0;
}
Listing 4.18. The functionrecursion.m program.
#include <stdio.h>
int factorial(int value);
int main()
{
printf("6! = %i\n", factorial(6));
return 0;
}
int factorial(int value)
{
if (value == 1) {
return value;
} else {
return value * factorial(value - 1);
}
}
Listing 4.19. Starting functionpointers.m.
#include <stdio.h>
void printem(void);
void caller_function(void (*pointer_to_
function)(void));
int main()
{
caller_function(printem);
return 0;
}
void printem(void)
{
printf("Hello there");;
}