C/C ++ function declaration and Function Definition (example)

Function-declaration, definition, and call

1. If the function is not declared, define it before calling:

#include　<stdio.h>

/* Define a big value function */
Int MAX (int x, int y ){
If (x> y)
Return x;
Else
Return y;
}

/* Define a small value function */
Int MIN (int x, int y ){
Return x <y? X: y;
}

int　main(void)
{
　　int　a　=　5;
　　int　b　=　6;

/* Call a function */
Printf ("% dn", MAX (a, B ));
Printf ("% dn", MIN (a, B ));
　　　　
Getchar ();
Return 0;
}

2. You can declare in the function header:

#include　<stdio.h>

int　main(void)
{
　　int　a　=　5;
　　int　b　=　6;

/* Declare the function to be used in the function header */
Int MAX (int x, int y );
Int MIN (int x, int y );
　　
/* Call a function */
Printf ("% dn", MAX (a, B ));
Printf ("% dn", MIN (a, B ));
　　　　
Getchar ();
Return 0;
}

/* Define a big value function */
Int MAX (int x, int y ){
If (x> y)
Return x;
Else
Return y;
}

/* Define a small value function */
Int MIN (int x, int y ){
Return x <y? X: y;
}

3. But should be declared in the file header:

The Declaration of the function prototype is declared in the header file (*. h) in actual use.

#include　<stdio.h>

/* Declare the function to be used in the file header */
Int MAX (int x, int y );
Int MIN (int x, int y );
　　
Int main (void)
{
Int a = 5;
Int B = 6;

/* Call a function */
Printf ("% dn", MAX (a, B ));
Printf ("% dn", MIN (a, B ));
　　　　
Getchar ();
Return 0;
}

/* Define a big value function */
Int MAX (int x, int y ){
If (x> y)
Return x;
Else
Return y;
}

/* Define a small value function */
Int MIN (int x, int y ){
Return x <y? X: y;
}

4. functions can be called, but cannot be nested:

#include　<stdio.h>

void　PrintSum(int　x,　int　y);
int　sum(int　x,　int　y);
　　
int　main(void)
{
　　PrintSum(1,2);　
　　PrintSum(111,222);　
　　
　　getchar();
　　return　0;
}

void　PrintSum(int　x,　int　y)　{
　　printf("%d　+　%d　=　%d;",　x,　y,　sum(x,y));
　　putchar('n');
}

int　sum(int　x,　int　y)　{
　　return　x　+　y;
}　

5. functions without parameters or returned values:

If the function does not have a parameter, it is best to use fun (void), but also fun;

If the function does not return a value, specify the return type as void;

Brackets are also required to call a function without parameters in c/c ++.

#include　<stdio.h>

void　prn(void);

Int main (void)
{
Prn ();/* call a function without parameters */
　　
Getchar ();
Return 0;
}

void　prn(void)　{
　　printf("okn");
}

6. When declaring a function, you can omit the form parameter:

#include　<stdio.h>

Int sum (int, int, int);/* omitted form parameter */

int　main(void)
{
　　printf("%dn",　sum(1,2,3));
　　
　　getchar();
　　return　0;
}

int　sum(int　x,　int　y,　int　z)
{
　　return(x　+　y　+　z);
}

7. Generally, the number of function parameters should not exceed 7:

However, C 99 supports up to 127 parameters.

#include　<stdio.h>

int　sum(int,　int,　int,　int,　int,　int,　int);

int　main(void)
{
　　printf("%dn",　sum(1,2,3,4,5,6,7));
　　
　　getchar();
　　return　0;
}

int　sum(int　a,　int　b,　int　c,　int　d,　int　e,　int　f,　int　g)
{
　　return(a　+　b　+　c　+　d　+　e　+　f　+　g);
}