冒泡排序程序返回随机数

Question

I'm learning C and my bubble sort code returns a random number sometimes (although sometimes it does returns the correct array numbers).

For example, it should print {0, 1, 3, 10}. But sometimes prints things like {-487420160, 0, 1, 3} or {-1484260208, 0, 1, 3} (only the first number changes, the other are correct).

This is the code:

#include <stdio.h>

int main(){

//array and variables
int arr[] = {1, 3, 0, 10};
int len = sizeof(arr)/ sizeof(int);
int j = 0;
int i = 0;

//print original array
printf("ORIGINAL ARRAY: \n");
printf("{");
for (int x = 0; x < len; x ++){
    printf("%d", arr[x]);
    if (x < len-1){
        printf(", ");
    }
}
printf("}\n");

//sorting
for ( i = 0;i < len; i++){
    for (j = 0 ;j < len; j ++){
        if(arr[j] > arr[j+1]){
            int temporal = arr[j];
            arr[j] = arr[j+1];
            arr[j+1] = temporal;
        }
    }
}

//print sorted array
printf("BUBBLE-SORTED ARRAY: \n");
printf("{");
for (int y = 0; y < len; y ++){
    printf("%d", arr[y]);
    if (y < len-1){
        printf(", ");
    }
}
printf("}\n");

return 0;
}

Do anybody know why or can help me improve the code?

Answer 1

In place of the for(j=0:j<len;j++) change to for(j=0:j<len-1;j++) :

for ( i = 0;i < len; i++){
    for (j = 0 ;j < len; j ++){// here instead of len use len-1
        if(arr[j] > arr[j+1]){
            int temporal = arr[j];
            arr[j] = arr[j+1];
            arr[j+1] = temporal;
        }
    }
}

Now, in bubble sort we usually compare until the end, but in your case when j=len then j+1 is a random number which has no existence and there is no element.

Make the following change and you will get the solution.

#include <stdio.h>

int main(){

//array and variables
int arr[] = {1, 3, 0, 10};
int len = sizeof(arr)/ sizeof(int);
int j = 0;
int i = 0;
int x=0;
int y=0;

//print original array
printf("ORIGINAL ARRAY: \n");
printf("{");
for (x = 0; x < len; x ++){
    printf("%d", arr[x]);
    if (x < len-1){
    printf(", ");
    }
}
printf("}\n");

//sorting
for ( i = 0;i < len; i++){
    for (j = 0 ;j < len-1; j++){// Here is the change, len has been changed to len-1
    if(arr[j] > arr[j+1]){
        int temporal = arr[j];
        arr[j] = arr[j+1];
        arr[j+1] = temporal;
    }
    }
}

//print sorted array
printf("BUBBLE-SORTED ARRAY: \n");
printf("{");
for (y = 0; y < len; y ++){
    printf("%d", arr[y]);
    if (y < len-1){
        printf(", ");
    }
}
printf("}\n");

return 0;
}