c - 如何让我的随机函数工作？

Question

随机函数在参数集中不起作用，我不知道为什么。谁能帮忙？我需要 18 到 38 之间的随机数，但我似乎无法得到它，我也不知道为什么。

这是我的代码

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

struct tires
{
    char Manufacturer[40];
    int tire_pressure[2];
    int pressure_change;
}typedef tires;

void getTireInformation(tires*, int);
void tirePressure(tires*, int);
int main()
{
    tires tire[4];
    tires* ptire = &tire[0];

    getTireInformation(ptire, 4);
    tirePressure(ptire, 4);

    return 0;
}

void getTireInformation(tires* ptire, int size)
{
    int i = 0;
    for (i = 0; i < size; i++)
    {
        printf("please enter Make for the tire: \n");
        scanf("%s", &(ptire + i) ->Manufacturer);
    }

    printf("all tire make you entered ...just for verification:\n");
    for(i = 0; i < size; i++)
        printf("%s\n",(ptire +i) ->Manufacturer);
}

void tirePressure(tires* ptire, int size)
{
    int i = 0;
    int min = 18;
    int max = 38;
    for (i = 0; i < size; i++)
    {
        srand(time(NULL));
        ptire = rand()%(max - min)-min;
        printf("%d\n", (ptire + i) -> tire_pressure);
    }
}

---

编辑:这是我在进行建议修复后更新的函数

void tirePressure(tires* ptire, int size)
{
    int i = 0;
    int min = 18;
    int max = 38;
    for (i = 0; i < size; i++)
    {
        ptire = rand()%(max - min + 1) + min;
        printf("%d\n", (ptire + i) -> tire_pressure);
    }
}

Answer 1

不必每次生成随机数时都调用srand(time(NULL));。将它放在 main() 中，在任何函数调用之前。

然后改变

rand() % (max - min) - min;

到

rand() % (max - min + 1) + min;

假设 max = 3 和 min = 1，你需要 rand() % 3 + 1 来生成一个从 1 到3 包括在内。

还有一个与随机数生成无关的问题:生成的随机数分配给ptire，即你分配的是一个tires* 与 int!

---

我已经完善了您的代码。希望它会起作用:

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

struct tires
{
    char Manufacturer[40];
    int tire_pressure[2];
    int pressure_change;
} typedef tires;

// Prototypes
void getTireInformation(tires*, size_t);
void tirePressure(tires*, size_t);

int main()
{
    tires tire[4];
    tires* ptire = &tire[0];

    srand(time(NULL));
    getTireInformation(ptire, 4);
    tirePressure(ptire, 4);

    return 0;
}

void getTireInformation(tires* ptire, size_t size)
{
    size_t i = 0;
    for (i = 0; i < size; i++)
    {
        printf("Please enter the maker of the tire: \n");
        scanf("%s", (ptire + i) -> Manufacturer); // just use str. &str actually causes undefined bahavior
    }

    printf("All tire make you entered ...just for verification:\n");
    for(i = 0; i < size; i++)
        printf("%s\n", (ptire +i) -> Manufacturer);
}

void tirePressure(tires* ptire, size_t size)
{
    int i = 0;
    int min = 18;
    int max = 38;
    for (i = 0; i < size; i++)
    {
        (ptire + i) ->tire_pressure[0] = rand() % (max - min + 1) + min;
        printf("%d\n", (ptire + i) -> tire_pressure[0]);
    }
}

这是我运行时的结果:

Please enter the maker of the tire: 
qwert
Please enter the maker of the tire: 
fewqwe
Please enter the maker of the tire: 
hcgexf
Please enter the maker of the tire: 
zrbghcr
All tire make you entered ...just for verification:
qwert
fewqwe
hcgexf
zrbghcr
22
34
31
31

现在所有数字都在 18 到 38 之间。请注意，tire_pressure 是一个包含两个 int 的数组。不知道你的目的，我只是给它的第一个元素随机数。