#include <stdio.h>
//a{n} = -6a{n-1} -9a{n-2}, a{1}=1, a{2}=2(再帰あり版)
 
int c = 0;  // 1. グローバル変数 c(recの呼び出し回数)
 
int rec(int n){
    c++;    // 2. recが実行されるたびに c を増やす
    if(n == 1){
        return 1;
    }
    else if(n == 2){
        return 2;
    }
    else{
        return -6*rec(n-1) - 9*rec(n-2);
    }
}
 
int main(void) {
    int n = 4;
    printf("数列a%dの値は%d\n", n, rec(n));
    printf("recの呼び出し回数は%d回\n", c);  // 3. c を表示
    return 0;
}

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