急一个小小的c程序请教……

Problem Description
A number sequence is defined as follows:
f(1) = 1, f(2) = 1, f(n) = (A * f(n - 1) + B * f(n - 2)) mod 7.
Given A, B, and n, you are to calculate the value of f(n).

Input
The input consists of multiple test cases. Each test case contains 3 integers A, B and n on a single line (1  <= A, B  <= 1000, 1  <= n  <= 100,000,000). Three zeros signal the end of input and this test case is not to be processed.

Output
For each test case, print the value of f(n) on a single line.

#include  <stdio.h>  
int main()  
{
int A,B,n,i,f1=1,f2=1,f3;
while(scanf("%d %d %d",&A,&B,&n)!=EOF);
{
for(i=1;i <=n;i++)
{
if(i==1 ? ?i==2)
f3=1;
else
f3=(A*f2+B*f1)%7;
f1=f2;f2=f3;
}
printf("%d\n",f3);
}
}
要怎么改才正确呢？
----------------解决方案--------------------------------------------------------
#include  <stdio.h>  
int main()  
{
int A,B,n,i,f1=1,f2=1,f3;
while(scanf("%d %d %d",&A,&B,&n)!=EOF);  //这里怎么有个小逗号？？？
{
for(i=1;i <=n;i++)
{
if(i==1 ? ?i==2)   //或应该是： ||   ，中间没有空格的
f3=1;
else
f3=(A*f2+B*f1)%7;
f1=f2;f2=f3;
}
printf("%d\n",f3);
}
}
----------------解决方案--------------------------------------------------------