t

1. Recursion
• 5! = 5 * 4 * 3 * 2 * 1
• 5! = 5 * 4!
• 4! = 4 * 3!...
n ! =
1
n*(n-1)! （n>1）
s=1;
n=1;
while (n<=20)
s = n * s;
n! = n * (n-1)!

2. Recursion
#include <stdio.h>
long fac(int n) {
long f;
if (n==0||n==1)
f=1;
else
f=n*fac(n-1);
printf("t%d!=%ldn", n, f);
return f;
}
void main( ) {
printf("nt5!=%ldn", fac(5));
}
1!=1
2!=2
3!=6
4!=24
5!=120
5!=120

3. Recursion
5!
5*4!
4*3!
3*2!
2*1!
1
120
5*24
4*6
3*2
2*1
1

4. Recursion
0 1 1 2 3 5 8 …
• fib(n) = fib(n-1) + fib(n-2)
• fib(1) = 0
• fib(2) = 1

5. Storage Classes
int a;
void main() {
int b;
…
}
int max(int x, int y) {
…
}

6. Automatic Storage
• Auto
• register
auto int a, b;
register int count = 1;

7. Static Storage
• static
• extern
static int a, b;
extern int total;

8. Automatic Variables and Static Variables
void func(int a) {
auto int b=10;
static int c=10;
b++; c++;
printf("a=%dtb=%dtc=%dn", a, b, c);
}
void main() {
int i;
for (i=1;i<=3;i++)
func(i);
}
a=1 b=11 c=11
a=2 b=11 c=12
a=3 b=11 c=13

9. Scope
function scope
file scope
block scope
function prototype scope

10. File Scope
int total；
int max(int, int);
void main() {
…
}
int limit;
int max（int x, int y） {
…
}

11. Function Scope
void main() {
…
loop:
…
goto loop;
}

12. Block Scope
int max(int x, int y) {
…
}
void main() {
int a;
…
{ int a;
…
}
…
}

13. Function Prototype Scope
int max(int x, int y);
void main() {
…
}
int max(int x, int y) {
…
}

14. Storage Classes And Scope
#include <stdio.h>
void a(void); /*function prototype*/
void b(void); /*function prototype*/
void c(void); /*function prototype*/
int x = 1; /*global variable*/
void main() {
int x = 5;
printf("local x in outer scope of main is %dn", x);
{ /*start new scope*/
int x = 7;
printf("local x in inner scope of main is %dn", x);
} /*end new scope*/
printf("nlocal x in outer scope of main is %dn", x);

15. Storage Classes And Scope
a();
b();
c();
a();
b();
c();
printf("local x in main is %dn", x);
}
void a() {
int x = 25; /*initialized each time a is called*/
printf("nlocal x in a is %d after enteringn", x);
x++;
printf("local x in a is %d before exitingn", x);
}

16. Storage Classes And Scope
void b() {
static int x = 50; /*static initialization only*/
/*first time b is called*/
printf("nlocal x in b is %d after enteringn", x);
x++;
printf("local x in b is %d before exitingn", x);
}
void c() {
printf("nglobal x is %d on entering cn", x);
x*=10;
printf("global x is %d on exiting cn", x);
}

17. Storage Classes And Scope
local x in outer scope of main is 5
local x in inner scope of main is 7
local x in outer scope of main is 5
local x in a is 25 after entering a
local x in a is 26 before exiting a
local x in b is 50 after entering b
local x in b is 51 before exiting b
global x is 1 on entering c
global x is 10 on exiting c

18. Storage Classes And Scope
local x in a is 25 after entering a
local x in a is 26 before exiting a
local x in b is 51 after entering b
local x in b is 52 before exiting b
global x is 10 on entering c
global x is 100 on exiting c
local x in main is 5