bubble sort a character array in alphabetic order

问题:

I'm trying to bubble sort a character array in alphabetic order. My code is as follows:

#define CLASS_SIZE 10
#include <stdio.h>

void bubbleSortAWriteToB(const char a[], char *b[]);

int main(void){
    char *s_letters[CLASS_SIZE];
    char letters[CLASS_SIZE] = {'a','r','p','b','r','c','x','e','w','j'};
    bubbleSortAWriteToB(letters,s_letters);
        return 0;
}

void bubbleSortAWriteToB(const char a[], char *b[]){
    char temp;
    int i,j;
    for(i=0;i<CLASS_SIZE-1;i++){
        for(j=1;j<CLASS_SIZE;j++){
            if((int)a[j-1]>(int)a[j]){
                temp = a[j];
                *b[j] = a[j-1];
                *b[j-1] = temp;

            }

    }

  }
}

It doesn't give any kind of error but when i run it it gets stuck like it's kinda in a inifinte loop. But from what i can see it isn't that either. Can you help me out?

回答1:

Fixing your code

First of all, there are some pretty serious fundamental issues with your code. Before we tackle those though, let's just fix what you have so far. Your sorting loop seemed to be half sorting the a array and half sorting the b array. you also never initialized the b array to contain any values. Here is a corrected version of your code:

#define CLASS_SIZE 10
#include <stdio.h>

void bubbleSortAWriteToB(const char a[], char * b[]);

int main(void){
    int i;

    // initialize array
    char * s_letters[CLASS_SIZE];
    char letters[CLASS_SIZE] = {'a','r','p','b','r','c','x','e','w','j'};
    // sort array
    bubbleSortAWriteToB(letters,s_letters);

    // print sorted array
    for (i=0;i<CLASS_SIZE;i++){
        printf("%c\n", *s_letters[i]);
    }

    return 0;
}

void bubbleSortAWriteToB(const char a[], char * b[]){
    char * temp;
    int i,j;

    // initialize b array to hold pointers to each element in a
    for (i=0;i<CLASS_SIZE;i++){
        b[i] = (char *)(a) + i;
    }

    // in-place sort the b array
    for(i=0;i<CLASS_SIZE;i++){
        for(j=i+1;j<CLASS_SIZE-1;j++){
            if(*b[j-1]>*b[j]){
                temp = b[j];
                b[j] = b[j-1];
                b[j-1] = temp;
            }
        }   
    }
}

The fix was to initialize the b array with points to a, and then sort the b array in-place by comparing the corresponding values in the a array.

---

Simplifying the code

In your original code, the strategy was to have an array of pointers (b) that would point to the elements in a, and then get sorted. This was unnecessary here though, because characters are smaller than pointers, so letting b be an array of characters is more space-efficient and simpler.

Also, your spacing was very squished-together and somewhat difficult to read. Here's a solution that uses b as an array of characters instead of pointers, and offers improved spacing. Also, declaring the function above was not necessary. It suffices to define the function and declare it once.

#define CLASS_SIZE 10
#include <stdio.h>

void bubbleSortAWriteToB(const char a[], char b[]){
    char temp;
    int i,j;

    // initialize b array to hold pointers to each element in a
    for (i = 0; i < CLASS_SIZE; i++){
        b[i] = a[i];
    }

    // in-place sort the b array
    for(i = 0; i < CLASS_SIZE; i++){
        for(j = i + 1; j < CLASS_SIZE - 1; j++){
            if(b[j-1] > b[j]){
                temp = b[j];
                b[j] = b[j-1];
                b[j-1] = temp;
            }
        }   
    }
}

int main(void){
    int i;

    // initialize array
    char s_letters[CLASS_SIZE];
    char letters[CLASS_SIZE] = {'a','r','p','b','r','c','x','e','w','j'};

    // sort array
    bubbleSortAWriteToB(letters, s_letters);

    // print sorted array
    int i;
    for (i = 0; i < CLASS_SIZE; i++){
        printf("%c\n", s_letters[i]);
    }

    return 0;
}

回答2:

Your s_letters is not properly initialized, yet you access it in:

*b[j] = a[j-1];
*b[j-1] = temp;

It's a segfault.

回答3:

I compiled this with gcc -g and ran it through Valgrind, and got this:

==54446==  Non-existent physical address at address 0x100000000
==54446==    at 0x100000EB0: bubbleSortAWriteToB (x.c:20)
==54446==    by 0x100000DFE: main (x.c:9)

Line 20 is this:

*b[j] = a[j-1];

char *b[] is an array of char pointers, but you're trying to put something in the pointers without initializing them. If you really want to do this, you'd need to:

b[j] = malloc(sizeof(*b[j])); // Create some space for a char
*b[j] = a[j-1]; // Put the char in that space

But, I don't think that's what you actually want. If you just change it to char b[], and remove all of your *'s, it works fine.

回答4:

Bubble sort

Console: Input: "face321" OutPut: "123acef"

    #include <stdio.h>

int main(){

    char c[80] = "0";
char temp = '0';
int offSet = 0;
int i = 0;
int j =0;
int count =0;

printf("Enter first string: ");
gets(c);

while (*(c + offSet) != '\0') {
    count++;
    offSet++;
}



for (i = 0; i < count; i++) {
for (j = 0; j < count - 1; j++) {


    if (c[j]>c[j + 1]) {

        temp = c[j];
        c[j] = c[j + 1];
        c[j + 1] = temp;

    }

}

}
    puts(c);
    return 0;
}