min（）函數的副作用

Question

我不明白爲什麼無意中修改了[i]的值？由註釋標記的行只能修改數組p的值，而不能修改數組的值。我已經注意到數組的值正在被修改爲副作用。我無法弄清楚爲什麼。

#include <iostream> 
#include <unordered_map> 

using namespace std; 

int main() { 
    unsigned int N, Q, K; 
    unsigned int a[N], p[N][N]; 
    unordered_map<unsigned int, unsigned int> counts_vector; 
    cin >> N; 
    for (unsigned int i = 0; i < N; i++) { 
     cin >> a[i]; 
     p[i][i] = a[i]; 
     for (unsigned int j = 0; j < i; j++) { 
      p[j][i] = min(p[j][i - 1], a[i]); // why is the value of a[i] getting modified? 
     } 
    } 
    for (unsigned int k = 0; k < N; k++) { 
     cout << "a: "<<a[k]<< endl; 
    } 
} 

Answer 1

在給出N值之前，您不應該聲明unsigned int a[N], p[N][N];！

變化

unsigned int N, Q, K; 
unsigned int a[N], p[N][N]; 
unordered_map<unsigned int, unsigned int> counts_vector; 
cin >> N; 

到

unsigned int N, Q, K; 
cin >> N; 
unsigned int a[N], p[N][N]; 
unordered_map<unsigned int, unsigned int> counts_vector;