http://www.eyny.com/viewthread.php?tid=5513814

gistfile1.c

#include<stdio.h>
void ThisIsFunction(int number);
int main(void)
{
	int num;
	printf("請輸入一個整數");
	scanf("%d",&num);
	ThisIsFunction(num);
	return 0;
}
void ThisIsFunction(int number)
{
	if ( number < 0 )
		printf("%d\n", -number);
	else
		printf("%d\n", number);
}