presentage in C programming

1.how to three subject presentage in c programming

#include<stdio.h>
#include<conio.h>
int per(float a,float b,float c);
void main()
{
int x,y,z;
float n;
clrscr();
printf("enter mark of 3 sub;");
scanf("%d%d%d",&x,&y,&z);
n=per(x,y,z);
printf("persentage=%f",n);
getch();
}
      int per(float a,float b,float c)
      {
      float per;
      per=((a+b+c)*100)/300;
      return(per);
      }