我正在尝试在for循环中执行if语句,它给了我以下问题:"错误c2106:' =' :左操作数必须是I值"在我的每个if循环旁边。
#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
// Function of given equation
double function(double x)
{
double result;
result = 0.2+25*x-200*pow(x,2)+675*pow(x,3)-900*pow(x,4)+400*pow(x,5);
return result;
}
int main()
{
double boundup; // Upper bound
double bounddown; // Lower bound
double n; // Number of intervals
double step; // Step size
double fsimp; // Simpson's rule
double ftrap; // Trapezoidal rule
cout << "Enter lower bound: " ;
cin >> bounddown;
cout << "Enter upper bound: " ;
cin >> boundup;
cout << "Number of intervals: " ;
cin >> n;
// Vector class for both x and fx
vector<double> x(n+1);
vector<double> fx(n+1);
// Define first and last values in x and fx because they will not change
step = (boundup-bounddown)/n;
x[0] = bounddown;
x[n] = boundup;
fx[0] = function(x[0]);
fx[n] = function(x[n]);
fsimp = fx[0];
for (int i=0; i<n; i++)
{
x[i+1] = x[i]+step;
fx[i+1] = function(x[i+1]);
if (i%2=0)
{
fsimp = 2*fx[i+1] + fsimp;
}
if (i%2=1)
{
fsimp = 4*fx[i+1] + fsimp;
}
fsimp = fx[n] + fsimp;
}
cout << "Bounds of integration: " << bounddown << ", " << boundup << endl;
cout << "Number of intervals: " << n << '\n' << endl;
cout << "Integral value of f(x): " << fsimp << endl;
return 0;
}
我只是想用Simpson的规则进行数值积分。我不确定如果发表声明我会怎么做。
答案 0 :(得分:6)
您需要使用比较(==
),而不是分配(=
):
if (i%2=0)
{
fsimp = 2*fx[i+1] + fsimp;
}
应该是:
if (i%2 == 0)
{
fsimp = 2*fx[i+1] + fsimp;
}