用C++语言写一段程序，输出第n个Fibonacci数。说明： Fibonacci数依次为：1，1，2，3，5，8，……，其规律为: Fi=1 (n=1) F2=1 (n=2) Fn=Fn-1+Fn-2 (n>=3)

Sure, here is a simple C program to output the nth Fibonacci number:

#include <stdio.h>

int fibonacci(int n);

int main() {
    int n;
    printf("Enter the value of n: ");
    scanf("%d", &n);
    printf("The %dth Fibonacci number is %d\n", n, fibonacci(n));
    return 0;
}

int fibonacci(int n) {
    if (n == 1 || n == 2) {
        return 1;
    } else {
        return fibonacci(n-1) + fibonacci(n-2);
    }
}

Please note that this program assumes that the user enters a positive integer value for n.