Code
```cpp
#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100 + 5;
double a[MAXN][MAXN];
double eps = 1e-8;
int n;
void Swap(int x, int y) {for (int i = 0; i < n + 1; i++) swap(a[x][i], a[y][i]);}
void Find(int x) {
int maxi = x;
for (int i = x + 1; i < n; i++) {
if (abs(a[i][x]) > abs(a[maxi][x])) maxi = i;
}
Swap(maxi, x);
}
void check1() {
for (int i = 0; i < n; i++) {
for (int j = 0; j < n + 1; j++) {
cout << a[i][j] << " ";
}
cout << '\n';
}
cout << '\n';
}
int check() {
for (int i = 0; i < n; ++i) {
if (fabs(a[i][n]) > eps) {
bool f = 1;
for (int j = 0; j < n; ++j) {
if (fabs(a[i][j]) > eps) f = 0;
}
if(f) return -1;
}
}
return 0;
}
int main() {
ios_base :: sync_with_stdio(0), cin.tie(0), cout.tie(0);
cin >> n;
bool f = 0;
for (int i = 0; i < n; i++) {
for (int j = 0; j < n + 1; j++) {
cin >> a[i][j];
}
}
for (int i = 0; i < n; i++) {
Find(i);
double xx = a[i][i];
if (fabs(xx) < eps) {
f = 1;
continue;
}
// check1();
for (int j = i; j < n + 1; j++) { //变成1
a[i][j] /= xx;
}
for (int j = i + 1; j < n; j++) { //第i项消成0
double x = a[j][i];
for (int k = 0; k < n + 1; k++) {
a[j][k] -= x * a[i][k];
}
}
}
// for (int i = n - 1; i >= 0; i--) {
// for (int j = 0; j < i; j++) {
// a[j][n] -= a[j][i] * a[i][n];
// a[j][i] = 0;
// }
// }
for (int j = n - 1, k = n - 1; j > -1; --j) { //j为行,k为列
if (fabs(a[j][k]) > eps) {
for (int i = 0; i < j; ++i) {
a[i][n] -= a[i][k] * a[j][n];
a[i][k] = 0;
}
--k;
}
}
if (f) {
cout << check() << '\n';
return 0;
}
for (int i = 0; i < n; i++) {
cout <<'x' << i + 1 << '=' << fixed << setprecision(2) << a[i][n] << '\n';
}
return 0;
}
```
by GoldenFishX @ 2024-01-10 16:52:22
@[_RSY_](/user/46197)
by GoldenFishX @ 2024-01-10 17:01:52
@[Maxmilite](/user/274993)
by GoldenFishX @ 2024-01-10 17:17:40
@[Big_Caibi](/user/156353) Added, thx.
by Maxmilite @ 2024-01-10 17:28:35