大哥大姐们，帮小妹做个题目，想了好久也想不出解决方案

大哥大姐们，帮小妹做个题目，想了好久也想不出
问题：

实现一维数组A(M)元素值循环左移两位，A=(1   2   3     4   5   )-----> A=(3   4   5   1   2   )  

先谢过了！

[解决办法]
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

float f( int );

int main()
{
FILE *fp;
int n;
char *file_name = "out.dat ";

printf( "Input n:\n ");
scanf( "%d ",&n);

if((fp = fopen(file_name, "w ")) == NULL)
printf( "Io error!\n ");
else fprintf(fp, "%.6f ",f(n));

fclose(fp);
printf( "Complete Succesfully\n ");
system( "pause ");
return 0;

}

float f(int n)
{
int sum = 0;
for (; n > 0;--n)
{
if ((n%3 == 0) && (n%7 == 0))
sum =sum + n;
}

return sqrt(sum);
}