求c中二维数组一列的最大和

Question

我有一个二维数组，我想对列求和，然后求和的最大值。我使用 malloc 作为数组进行初始化。当程序完成时我想打印结果，但结果与我期望的不同。

结果->

2 sum is -> 2 max is -> 4201200
5 sum is -> 7 max is -> 4201200
6 sum is -> 13 max is -> 4201200
8 sum is -> 8 max is -> 4201200
9 sum is -> 17 max is -> 4201200
6 sum is -> 23 max is -> 4201200
5 sum is -> 5 max is -> 4201200
9 sum is -> 14 max is -> 4201200
2 sum is -> 16 max is -> 4201200
max is 4201200 column 0

这是我的代码--->

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {

    int row = 3, col = 5;
    int *a = (int *)malloc(row * col * sizeof(int));

    int i, j;
    for (i = 0; i < row; i++)
        for (j = 0; j < col; j++)
            *(a + i * col + j) = (rand() % (10 - 1 + 1)) + 1;   

    printf("The array elements are:\n");
    
    int sad;
    int max1;
    int sum = 0;
    for (i = 0; i < row; i++) {
        for (j = 0; j < row; j++) {
            printf("%d ", a[j * col + i]);
            sum += a[j * col + i];
            printf("sum is -> %d max is -> %d\n", sum, max1);
        }
        if (sum > max1) {
            printf("max is detected");
            max1 = sum;
            sad = j;
            sum = 0;
        }
        sum = 0;
    }
    printf("max is %d column %d", max1, sad);
    free(a);
    return 0;
}

谢谢！

Answer 1

max1 未初始化，因此测试 if (sum > max1) 没有意义并且 max1 可能无法正确更新。在你的例子中，max1 恰好有值 4201200，但行为是未定义的，这可能是任何值，甚至是某些系统上的陷阱值。

由于所有矩阵元素都是正数，可以将max1初始化为0，否则就使用<limits.h>中定义的INT_MIN或者为第一个添加测试列。

另外，在第二个循环中索引值i和j被交换了，循环测试也不正确。

这是修改后的版本：

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {

    int rows = 3, cols = 5;
    int *a = (int *)malloc(rows * cols * sizeof(int));

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            a[i * cols + j] = (rand() % (10 - 1 + 1)) + 1;   
        }
    }

    printf("The array elements are:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf(" %2d", a[i * cols + j]);
        }
        printf("\n");
    }
    
    int max_col = 0;
    int max_sum = 0;
    for (int j = 0; j < cols; j++) {
        int sum = 0;
        for (int i = 0; i < rows; i++) {
            sum += a[i * cols + j];
        }
        printf("sum of column %i is -> %d\n", j, sum);
        if (j == 0 || sum > max_sum) {
            printf("max is detected\n");
            max_sum = sum;
            max_col = j;
        }
    }
    printf("max is %d column %d\n", max_col, max_sum);
    free(a);
    return 0;
}

求c中二维数组一列的最大和

Find the maximum sum of a column of two dimensional arrays in c

arrays

c

algorithm

pointers

malloc