宣告與呼叫

1. 函式可以放在程式的任意位置，放在呼叫敘述之前，可以不用先宣告，但若放在呼叫敘述之後，則必須先宣告。宣告語法：

   return_type function_name( parameter list );
   

2. 宣告範例

   int max(int num1, int num2);
   int max(int, int);
   

3. 呼叫範例

   [dywang@deyu zzz]$ vim function1.c
   [dywang@deyu zzz]$ cat function1.c
   #include <stdio.h>
   
   int max(int num1, int num2) {
      int result;
   
      if (num1 > num2) result = num1;
      else result = num2;
      return result;
   }
   
   main() {
   	int a, b;
   
   	printf("Enter TWO integers: ");
   	scanf("%d %d", &a, &b);
   
   	printf("a = %d, b = %d, max = %d\n", a, b, max(a,b));
   }
   

4. 編譯成功

   [dywang@deyu zzz]$ gcc -o function1 function1.c
   

5. 執行結果

   [dywang@deyu zzz]$ ./function1
   Enter TWO integers: 10 20
   a = 10, b = 20, max = 20
   [dywang@deyu zzz]$ ./function1
   Enter TWO integers: 21 11
   a = 21, b = 11, max = 21