填充动态分配的二维数组

Question

我正在尝试填充动态分配的二维数组。

具体来说，我正在尝试将随机数输入到数组中。

代码如下：

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

int main(void)
{

int i, j, num_students = 10, num_grades = 4;
int **array;

srand(time(NULL));


array = malloc(sizeof(int *) * num_students);

for (i = 0; i < num_students; ++i)
    array[i] = malloc(sizeof(int) * num_grades);

for (i = 0; i < num_students; ++i)
{
    printf("Student %d has grades: ", i);
    for (j = 0; j < num_grades; ++j)
        array[i][j] = rand() % 101;
        printf("%d ", array[i][j]);

    printf("\n");
    free(array[i]);
}

free(array);

return 0;

}

输出：

Student 0 has grades: 0 
Student 1 has grades: 0 
Student 2 has grades: 0 
Student 3 has grades: 0 
Student 4 has grades: 0 
Student 5 has grades: 0 
Student 6 has grades: 0 
Student 7 has grades: 0 
Student 8 has grades: 0 
Student 9 has grades: 0 

我不知道为什么它打印的是 0 而不是随机数。

Answer 1

你错过了{ ... }...

for (j = 0; j < num_grades; ++j)
        array[i][j] = rand() % 101;
        printf("%d ", array[i][j]);

和

一样

for (j = 0; j < num_grades; ++j) {
        array[i][j] = rand() % 101;
}
printf("%d ", array[i][j]);

，但应该是

for (j = 0; j < num_grades; ++j) {
        array[i][j] = rand() % 101;
        printf("%d ", array[i][j]);
}

Answer 2

您在内部 for 循环周围缺少括号：

for (j = 0; j < num_grades; ++j)
{
    array[i][j] = rand() % 101;
    printf("%d ", array[i][j]);
}

Answer 3

缩进不控制你的范围（例如在 Python 中）。您的 for 循环仅迭代第一行：

for (j = 0; j < num_grades; ++j)
    array[i][j] = rand() % 101; // <- only this is iterated over
    printf("%d ", array[i][j]); // <- this only runs once, after the for-loop

确保您已将两行都封装在大括号中：

for (j = 0; j < num_grades; ++j) {
    array[i][j] = rand() % 101;
    printf("%d ", array[i][j]);
}