如果参数类型省略，默认为int类型。（此为古老写法）

#include<stdio.h>float average(a,n)
int a[];
{int j;float s=0;float aver;for(j=0;j<=0;j++){s+=a[j];}aver=s/n;return aver;
}main()
{int a[12]={10,4,2,7,3,12,5,34,5,9,6,8};printf("the average is:%.2f",average(a,12));
}

#include<stdio.h>int test(a,b)
{return a+b;
}
main()
{int a=test(1,2);printf("%d",a);
}