當運行代碼時它不響應（但它在後臺運行正常）

Question

我構建了一個程序來顯示警衛的行爲。首先有100個（我在代碼中放10個，因爲更容易發現錯誤）（1到100個）燈。起初，他們都在，但： -

1. 他經過他們第一次後，他把他們全部關閉。
2. 第二次經過他們之後，他改變了燈號 ，這些燈號代替了2及其倍數（2 4 6 8 ...） - ，這些燈號是現在開啓的，而相反的。
3. 第三次他改變了第三名和 3（3 6 9 ....）的倍數 - 那些現在和現在相反的人。
4. 第四時間他改變在第四位的那些和 4的倍數（4 8 12 ....）

程序顯示許多燈如何在端部均關閉。 現在我構建的代碼編譯器顯示沒有警告或錯誤，但運行時它會停止響應。 （編譯器設置爲顯示所有警告。）

有沒有人知道代碼有什麼問題？

#include<stdio.h> 
#define N 100 
int firstwalk(int light[N]); 
int secondtwalk(int light[N]); 
int thirdtwalk(int light[N]); 
int fourthtwalk(int light[N]); 
int main() 
{ 
    int light[N] = {0}; 
    int i; 
    for (i = 0;i < N;i++) 
    { 
     light[i] = 1; 
    } 
    printf("Lights before the first walk- "); 
    for (i = 0;i < N;i++) 
    { 
     printf("%d ", light[i]); 
    } 
    firstwalk(light); 
    secondtwalk(light); 
    thirdtwalk(light); 
    fourthtwalk(light); 
    printf("the lights that were off are :- "); 
    for (i = 0;i < N;i++) 
    { 
     if (light[i] == 0) 
      printf("%d ", i+1); 
    } 

} 
int firstwalk(int light[N]) 
{ 
    int i; 
    for (i = 0;i < N;i++) 
    { 
     light[i] = 0; 
    } 
    printf("Lights after the first walk- "); 
    for (i = 0;i < N;i++) 
    { 
     printf("%d ", light[i]); 
    } 
    printf("\n"); 
    return light; 

} 
int secondtwalk(int light[N]) 
{ 
    int i; 
    for (i = 1;i < N;i= i * 2 + 1) 
    { 
     light[i] = 1; 

    } 
    printf("Lights after the second walk- "); 
    for (i = 0;i < N;i++) 
    { 
     printf("%d ", light[i]); 
    } 
    printf("\n"); 
    return light; 
} 
int thirdtwalk(int light[N]) 
{ 
    int i; 
    for (i = 2;i < N;i= i * 3 + 2) 
    { 
     if (light[i] == 1) 
      light[i] = 0; 
     else light[i] = 1; 
    } 
    printf("Lights after the third walk- "); 
    for (i = 0;i < N;i++) 
    { 
     printf("%d ", light[i]); 
    } 
    printf("\n"); 
    return light; 
} 
int fourthtwalk(int light[N]) 
{ 
    int i; 
    for (i = 3;i < N;i= i * 4 + 3) 
    { 
     if (light[i] == 1) 
      light[i] = 0; 
     else light[i] = 1; 
    } 
    printf("Lights after the third walk- "); 
    for (i = 0;i < N;i++) 
    { 
     printf("%d ", light[i]); 
    } 
    printf("\n"); 
    return light; 
} 

謝謝。

Answer 1

在你的代碼的主要缺陷基本上是你所訪問的陣列的方式，你會超越數組邊界的時候，這裏有一個可能的版本是固定：

#include <stdio.h> 

#define N 10 

void show_lights_all(char *label, int light[N]); 
void show_lights_off(char *label, int light[N]); 
void firstwalk(int light[N]); 
void secondtwalk(int light[N]); 
void thirdtwalk(int light[N]); 
void fourthtwalk(int light[N]); 

int main() { 
    int light[N] = {0}; 
    show_lights_all("Initial state of lights- ", light); 
    firstwalk(light); 
    secondtwalk(light); 
    thirdtwalk(light); 
    fourthtwalk(light); 
    show_lights_off("\nLights that were off are :- ", light); 
} 

void show_lights_all(char *label, int light[N]) { 
    printf(label); 
    for (int i = 0; i < N; i++) { 
     printf("%d ", light[i]); 
    } 
} 

void show_lights_off(char *label, int light[N]) { 
    printf(label); 
    for (int i = 0; i < N; i++) { 
     if (light[i] == 0) printf("%d ", i + 1); 
    } 
} 

void firstwalk(int light[N]) { 
    show_lights_all("\nLights before the first walk- ", light); 
    for (int i = 0; i < N; i++) { 
     light[i] = 0; 
    } 
    show_lights_all("Lights after the first walk- ", light); 
} 

void secondtwalk(int light[N]) { 
    show_lights_all("\nLights before the second walk- ", light); 
    for (int i = 1; i < N; i += 2) { 
     light[i] = 1; 
    } 
    show_lights_all("Lights after the second walk- ", light); 
} 

void thirdtwalk(int light[N]) { 
    show_lights_all("\nLights before the third walk- ", light); 
    for (int i = 2; i < N; i += 3) { 
     light[i] = light[i] == 1 ? 0 : 1; 
    } 
    show_lights_all("Lights after the third walk- ", light); 
} 

void fourthtwalk(int light[N]) { 
    show_lights_all("\nLights before the fourth walk- ", light); 
    for (int i = 3; i < N; i += 4) { 
     light[i] = light[i] == 1 ? 0 : 1; 
    } 
    show_lights_all("Lights after the fourth walk- ", light); 
} 

想想吧，假設你正在做類似for(int i=0;i<N;i++) light[i * 3 + 2]的事情，現在...當我= 3->光[11]，我= 4->光[14]，等等......並且您只分配了內存一個10個元素的數組。

一個更好的模式將被取代是這樣的：

for(int i=0;i<N;i++) light[i*k1+k2] 

通過類似：

for(int i=k2;i<N;i+=k1) light[i] 

這是它保證不會超出數組邊界

你之後」一個更安全的版本我已經理解了上面的解釋，下一步將會將代碼重構成不那麼冗長的東西：

#include <stdio.h> 

#define N 10 

#define LIGHTS_ALL -1 
#define LIGHTS_OFF 0 
#define LIGHTS_ON 1 

char *lights_str(int light[N], int status_light) { 
    char s[256] = {0}; 
    int n = 0; 

    for (int i = 0; i < N; i++) { 
     if (status_light == LIGHTS_OFF) { 
      if (light[i] == LIGHTS_OFF) n += sprintf(&s[n], "%d ", i); 
      continue; 
     } 
     if (status_light == LIGHTS_ON) { 
      if (light[i] == LIGHTS_ON) n += sprintf(&s[n], "%d ", i); 
      continue; 
     } 

     n += sprintf(&s[n], "%d", light[i]); 
    } 

    return s; 
} 

void firstwalk(int light[N]) { 
    for (int i = 0; i < N; i++) { 
     light[i] = 0; 
    } 
} 

void secondtwalk(int light[N]) { 
    for (int i = 1; i < N; i += 2) { 
     light[i] = 1; 
    } 
} 

void thirdtwalk(int light[N]) { 
    for (int i = 2; i < N; i += 3) { 
     light[i] = light[i] == 1 ? 0 : 1; 
    } 
} 

void fourthtwalk(int light[N]) { 
    for (int i = 3; i < N; i += 4) { 
     light[i] = light[i] == 1 ? 0 : 1; 
    } 
} 


int main() { 
    int light[N] = {0}; 
    char *walks[256] = {"first", "second", "third", "fourth"}; 

    void (*p[4])(int light[N]); 
    p[0] = firstwalk; 
    p[1] = secondtwalk; 
    p[2] = thirdtwalk; 
    p[3] = fourthtwalk; 
    for (int i = 0; i < 4; i++) { 
     printf("\nLights before the %s walk-\t%s", walks[i], 
       lights_str(light, LIGHTS_ALL)); 
     p[i](light); 
     printf("\tLights after the %s walk-\t%s", walks[i], 
       lights_str(light, LIGHTS_ALL)); 
    } 
    printf("\n\nFinal status\tLights on\t%s\tLights off\t%s", 
      lights_str(light, LIGHTS_OFF), lights_str(light, LIGHTS_ON)); 
} 

其實，不要停在這裏，試圖進一步重構，直到代碼變得越來越好...我會這個任務留給你:)