Thread: another sort useless program

it still stores the array sorted. can i store the size as a global variable so i can use it in other functions? is that what i should do? and if so how?

Code:

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

void sort(int array[]);

int main(int argc, char *argv[]){
    char answer[2] ;
    int num, c, size;
    int array[]={ 34, 12, 22, 109, 7, 6, 709, 100, 1, 4, 23,24};
  
    printf("%40s", "----------------\n");
    printf("%40s", " sort or unsort?\n");
    printf("%40s", "----------------\n");
    printf("\n");
    printf("would you like the numbers sorted or unsorted?\n");

    printf("type 1 for sorted. 2 for unsorted. q to quit\n");
    
    do{
         num = atoi(fgets(answer,sizeof(answer), stdin));
         //num = atoi(answer);
         size = sizeof(array) / sizeof(*array);
         
         switch(num){
         case 1:
         printf("%40s", "---------Sorted----------\n");
         sort(array);
         for(c = 0; c < size; c++)
         printf("%i\t",array[c]);
         printf("\n");
         break;
  
         case 2:
         printf("%40s", "------Unsorted-------\n");
         for(c = 0; c < size; c++)
         printf("%i\t",array[c]);
         printf("\n");
         break;
  }
         
  }while(answer[0] != 'q' );
   getchar();	
   return 0;
}

void sort(int array[]){
    int a, b, temp;
    for(a = 0; a < 12; a++)
    for(b = 0; b < 12; b++)
    if(array[a] < array[b]){
             temp = array[a];
             array[a] = array[b];
             array[b] = temp;
    }
}

Originally Posted by mrsirpoopsalot

can i store the size as a global variable so i can use it in other functions? is that what i should do? and if so how?

Code:

void sort(int array[]){
    int a, b, temp;
    for(a = 0; a < 12; a++)
    for(b = 0; b < 12; b++)
    if(array[a] < array[b]){
             temp = array[a];
             array[a] = array[b];
             array[b] = temp;
    }
}

Not necessarily global but local to main.

This code is quite inefficient.

The first iteration of the inner loop will be comparing array[0] against array[0] however the lowest value in the array will end up in array[0] at the end of the first iteration of the outer loop.

The second iteration of the outer loop will be comparing array[1] against array[0] followed by array[1] against array[1], neither of which are useful.

How about this, where you pass in the size of the array, limit the outer loop to checking up to the penultimate element, and start the inner loop from the next element after that which the outer loop is processing:

Code:

void sort(int array[], int elements){
    int a, b, temp;

    for(a = 0; a < elements - 1; a++)
       for(b = a + 1; b < elements; b++)
          if(array[a] < array[b]){
             temp = array[a];
             array[a] = array[b];
             array[b] = temp;
          }

Not necessarily global but local to main.

To expand on this, you could initialize the array in main() with no size in it. Then you could declare the size variable which is initialized to sizeof(array)/sizeof(*array). (You only have to do this once since the size of array isn't going to change.) You could then pass size to any functions that use array.

To expand on this, you could initialize the array in main() with no size in it. Then you could declare the size variable which is initialized to sizeof(array)/sizeof(*array). (You only have to do this once since the size of array isn't going to change.) You could then pass size to any functions that use array

Im a little confused about this. did i already do that?

Code:

int main(int argc, char *argv[]){
    char answer[2] ;
    int num, c, size;
    int array[]={ 34, 12, 22, 109, 7, 6, 709, 100, 1, 4, 23,24};

isnt that under main? sorry for the confusion =(
also

for(a = 0; a < elements - 1; a++)

i see -1 used alot in arrays and loops etc, but i never understood why its used?

also

Code:

sizeof(array)/sizeof(*array).

is the obove code merely taking the whole size of the array including all whitespace and then dividing the actual elements within it to get the size i want? couldnt i just do sizeof(*array) itself?

Originally Posted by mrsirpoopsalot

Im a little confused about this. did i already do that?

Code:

int main(int argc, char *argv[]){
    char answer[2] ;
    int num, c, size;
    int array[]={ 34, 12, 22, 109, 7, 6, 709, 100, 1, 4, 23,24};

isnt that under main? sorry for the confusion =(

Yes, you already did. I was looking at a previous post.

also

i see -1 used alot in arrays and loops etc, but i never understood why its used?

An array declared like so

Code:

int array[12];

has 12 elements, 0..11. array[12] isn't a valid index. So, for example, to access the last element in an array, if you know that the array has size elements, you would use array[size-1], which is the last addressable array element (if size is >0).

also

Code:

sizeof(array)/sizeof(*array).

is the obove code merely taking the whole size of the array including all whitespace and then dividing the actual elements within it to get the size i want? couldnt i just do sizeof(*array) itself?

sizeof(*array) would give the sizeof the first element in a array; 4 for an int (on a 32-bit computer), 1 for a char, etc. sizeof(array) gives the whole size of the entire array in memory. For a 12 element in array, it would be 12*4=48. Since you're trying to get the number of elements in the array, you divide the total size by the size of one of the elements. (Since sizeof(char) is always 1, if you're calaulating the sizeof a character array you can just use sizeof(array).)

Originally Posted by mrsirpoopsalot

also

Originally Posted by risby

for(a = 0; a < elements - 1; a++)

i see -1 used alot in arrays and loops etc, but i never understood why its used?

Originally Posted by dwks

An array declared like so

Code:

     int array[12];

has 12 elements, 0..11. array[12] isn't a valid index. So, for example, to access the last element in an array, if you know that the array has size elements, you would use array[size-1], which is the last addressable array element

What dwks has explained is good for why you use "a < elements" as the continuation condition of a for loop but the reason I used "a < elements -1" in the outer loop is because I was trying to get you to test all elements in the array except the last one against the next and subsequent elements. You can't check the last element against the next element because there isn't one. The code you have at the moment often checks an array element against itself!