输入一个n*n的double二维数组，用C语言找到它的对角矩阵，下三角矩阵，上三角矩阵。 输入： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 输出： diagonal: 1 0 0 0 0 0 7 0 0 0 0 0 13 0 0 0 0 0 19 0 0 0 0 0 25 upper triangular: 1 2 3 4 5 0 7 8 9 10 0 0 13 14 15 0 0 0 19 20 0 0 0 0 25 lower triangular: 1 0 0 0 0 6 7 0 0 0 11 12 13 0 0 16 17 18 19 0 21 22 23 24 25

下面是对角矩阵，下三角矩阵和上三角矩阵的C语言代码：

#include <stdio.h>

void printDiagonal(double arr[][5], int n){
    printf("diagonal:");
    int i, j;
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            if(i==j){
                printf(" %g", arr[i][j]);
            }else{
                printf(" %d", 0);
            }
        }
    }
    printf("\n");
}

void printLowerTriangular(double arr[][5], int n){
    printf("lower triangular:");
    int i, j;
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            if(j<=i){
                printf(" %g", arr[i][j]);
            }else{
                printf(" %d", 0);
            }
        }
    }
    printf("\n");
}

void printUpperTriangular(double arr[][5], int n){
    printf("upper triangular:");
    int i, j;
    for(i=0;i<n;i++){
        for(j=0;j<n;j++){
            if(j>=i){
                printf(" %g", arr[i][j]);
            }else{
                printf(" %d", 0);
            }
        }
    }
    printf("\n");
}

int main(){
    double arr[5][5]={
        {1,2,3,4,5},
        {6,7,8,9,10},
        {11,12,13,14,15},
        {16,17,18,19,20},
        {21,22,23,24,25}
    };
    printDiagonal(arr, 5);
    printLowerTriangular(arr, 5);
    printUpperTriangular(arr, 5);
    return 0;
}

上面的代码会输出以下结果：

diagonal: 1 0 0 0 0 0 7 0 0 0 0 0 13 0 0 0 0 0 19 0 0 0 0 0 25
lower triangular: 1 0 0 0 0 6 7 0 0 0 11 12 13 0 0 16 17 18 19 0 21 22 23 24 25
upper triangular: 1 2 3 4 5 0 7 8 9 10 0 0 13 14 15 0 0 0 19 20 0 0 0 0 25