C语言怎么计算程序所花时间

#include<stdio.h>
#include<iostream>
#include<stdlib.h>
#include<time.h>
using namespace std;
int main()
{
    clock_t cBegin = clock();
    int M = 1000000, N = 0,b=0,c=0,i=0;
    srand((unsigned)time(NULL));//srand 在stdlib.h中
    int* a;
    cout << "input N:";
    cin >> N;
    a = new int[M];
    for ( i=0;i<=M;i++)
    {
        b =  rand();
        a[i] = b;

        
    }
    for (int p = 0; p <= N; p++)
    {
         c = rand();
         for ( i = 0; i <= M; i++)
         {
             if (c == a[i])
                 cout << i<< endl;
         }
    }
    clock_t cEnd = clock();
    cout << "所花时间："<<cEnd - cBegin << endl;
    return 0;
}