首次调用diagonalSum(matrix,3)的返回值是：

cpp
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1///动态矩阵操作与递归求和
2#include <iostream>
3#include <vector>
4,[object Object],
5,[object Object],
6,[object Object],
7,[object Object],
cpp
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1int main() {,[object Object],
2int n = 3;,[object Object],
3int** matrix = createMatrix(n);,[object Object],
4cout << "主对角线和: " << diagonalSum(matrix, n) << endl;,[object Object],
5// 修改矩阵元素,[object Object],
6matrix[1][1] = 100;,[object Object],
7cout << "修改后对角线和: " << diagonalSum(matrix, n) << endl;,[object Object],
8freeMatrix(matrix, n);,[object Object],
9return 0;,[object Object],
10},[object Object],