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sorting an array of string

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sorting an array of string

 
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  #1
Jun 7th, 2004
is there any function that helps to sort an array of strings alphabeticly
i need to sort an array alphabeticly which contains names of students
thx 4 yr help
matika
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Re: sorting an array of string

 
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  #2
Jun 7th, 2004
void qsort ( void * base, size_t num, size_t width, int (*fncompare)(const void *, const void *) );
Sort using quicksort algorith.
This function uses an implementation of the quicksort algorithm to sort the num elements of an array pointed by base, each element has the specified width in bytes.
The method used to compare each pair of elements is provided by the caller to this function with fncompare parameter, that is a function called one or more times during the sort process.
Parameters.
-------------
base
Pointer to the first element of the array where the sorting process has to be performed.
num
Number of elements in the array pointed by base.
width
Width of each element in the array.
fncompare
Function that compares two elements. This should be provided by the caller to this function and must follow or be casted to a declaration like:

int fncompare (const void * elem1, const void * elem2 );
The function should receive two parameters (elem1 and elem2) that are pointers to elements, and should return an int value with the result of comparing them:

return value description
<0 *elem1 goes before *elem2
0 *elem1 == *elem2
>0 *elem1 goes after *elem2

Return Value.
(none)

Portability.
Defined in ANSI-C.

Example.
C Syntax (Toggle Plain Text) 
  1.  
  2. /* qsort example */
  3. #include <stdio.h>
  4. #include <stdlib.h>
  5.  
  6. int values[] = { 40, 10, 100, 90, 20, 25 };
  7.  
  8. int compare (const void * a, const void * b)
  9. {
  10.   return ( *(int*)a - *(int*)b );
  11. }
  12.  
  13. int main ()
  14. {
  15.   int * pItem;
  16.   int n;
  17.   qsort (values, 6, sizeof(int), compare);
  18.   for (n=0; n<6; n++)
  19.   {
  20.     printf ("%d ",values[n]);
  21.   }
  22.   return 0;
  23. }
  24.  
  25. Output:
  26. 10 20 25 40 90 100
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Re: sorting an array of string

 
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  #3
Jun 9th, 2004
:rolleyes: sorry but may be u did not understood my question
i need to sort an array of characters which contains names of students alphabeticly
and i'm asking if there is a function that do this job quickly (sorting the array of chararcters alphabeticly)
thx
matika
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Re: sorting an array of string

 
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  #4
Jun 9th, 2004
wait... are you trying to list names of students alphabetically or are you trying to change the characters in each students name around into alphabetical order?
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Re: sorting an array of string

 
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  #5
Jun 9th, 2004
hey,I will give you a direction.

You will first have to make a funtion which will compare 2 strings and say which one is greater by comparing the individual chars and returning when it hit's a char which is no equal to the other, like sad sam, (in this case m > d).

Put this into a sort algorithm.

[think this is not much help eh?,see what you can do and you might even suprise yourself.Sometimes just a direction can do wonders.If you still have problems post here,maybe with what you have coded and we will check it out.your will learn more if you do it yourself ]
See what you can, remember what you need

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Re: sorting an array of string

 
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  #6
Jun 9th, 2004
i'm trying to list names of students alphabetically
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Re: sorting an array of string

 
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  #7
Jun 9th, 2004
void arranging()
{
char
temp[30],
name[50][30];

float
temp1,
temp2,
temp3,
temp4,
temp5,
temp6,
grade1[50],
grade2[50],
grade3[50],
grade4[50],
grade5[50],
grade6[50];
int
i=0,
j,
y,
x,
n=0;;



ifstream fin("names.txt");
while(fin)
{
fin.getline(name[i],30);
i++;
}
fin.close();
ifstream finn("grades.txt");
while(finn)
{
finn>>grade1[n];
finn>>grade2[n];
finn>>grade3[n];
finn>>grade4[n];
finn>>grade5[n];
finn>>grade6[n];
n++;
}
finn.close();
for(y=0;y<i;y++)
{
for(j=y+1;j<i;j++)
{
if(name[j][0]<name[y][0])
{
for(x=0;x<30;x++)
{
temp[x]=name[j][x];
temp1=grade1[j];
temp2=grade2[j];
temp3=grade3[j];
temp4=grade4[j];
temp5=grade5[j];
temp6=grade6[j];
}
for(x=0;x<30;x++)
{
name[j][x]=name[y][x];
grade1[j]=grade1[y];
grade2[j]=grade2[y];
grade3[j]=grade3[y];
grade4[j]=grade4[y];
grade5[j]=grade5[y];
grade6[j]=grade6[y];

}
for(x=0;x<30;x++)
{
name[y][x]=temp[x];
grade1[y]=temp1;
grade2[y]=temp2;
grade3[y]=temp3;
grade4[y]=temp4;
grade5[y]=temp5;
grade6[y]=temp6;
}
}
}
}
for(y=0;y<i;y++)
{
for(j=y+1;j<i;j++)
{

if(name[j][0]==name[y][0])
{
if(name[j][1]<=name[y][1])
{
for(x=0;x<30;x++)
{
temp[x]=name[j][x];
temp1=grade1[j];
temp2=grade2[j];
temp3=grade3[j];
temp4=grade4[j];
temp5=grade5[j];
temp6=grade6[j];
}
for(x=0;x<30;x++)
{
name[j][x]=name[y][x];
grade1[j]=grade1[y];
grade2[j]=grade2[y];
grade3[j]=grade3[y];
grade4[j]=grade4[y];
grade5[j]=grade5[y];
grade6[j]=grade6[y];
}
for(x=0;x<30;x++)
{
name[y][x]=temp[x];
grade1[y]=temp1;
grade2[y]=temp2;
grade3[y]=temp3;
grade4[y]=temp4;
grade5[y]=temp5;
grade6[y]=temp6;
}
}
}

}
}
for(y=0;y<i;y++)
{
for(j=y+1;j<i;j++)
{
if(name[j][0]==name[y][0])
{
if(name[j][1]==name[y][1])
{
if(name[j][2]<name[y][2])
{
for(x=0;x<30;x++)
{
temp[x]=name[j][x];
temp1=grade1[j];
temp2=grade2[j];
temp3=grade3[j];
temp4=grade4[j];
temp5=grade5[j];
temp6=grade6[j];
}
for(x=0;x<30;x++)
{
name[j][x]=name[y][x];
grade1[j]=grade1[y];
grade2[j]=grade2[y];
grade3[j]=grade3[y];
grade4[j]=grade4[y];
grade5[j]=grade5[y];
grade6[j]=grade6[y];
}
for(x=0;x<30;x++)
{
name[y][x]=temp[x];
grade1[y]=temp1;
grade2[y]=temp2;
grade3[y]=temp3;
grade4[y]=temp4;
grade5[y]=temp5;
grade6[y]=temp6;
}
}
}
}
}
}
ofstream fout("names.txt");
for(x=1;x<i;x++)
{
fout<<name[x]<<endl;
}
fout.close();
ofstream fott("grades.txt");
for(x=1;x<i;x++)
{
fott<<grade1[x]<<" ";
fott<<grade2[x]<<" ";
fott<<grade3[x]<<" ";
fott<<grade4[x]<<" ";
fott<<grade5[x]<<" ";
fott<<grade6[x]<<endl;
}
fott.close();

}
that's what i wrote it suposes that it took the names from a file
this sort the names it only compares the 3 1st char in the name
i.e. it sort the names according to the 3 first characters
i didnt succed to compare all the characters of the name
if u can help i'll be thxful
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Re: sorting an array of string

 
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  #8
Jun 9th, 2004
C or C++?

The C solution is qsort, and the only difference from what was already shown is the comparison function you write.

In C++ there is a std::sort.
C Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. #include <vector>
  3. #include <algorithm>
  4. typedef std::vector<std::string>::iterator		 iter;
  5. typedef std::vector<std::string>::const_iterator  citer;
  6. void Show(std::vector<std::string> &alist, const char *label = "")
  7. {
  8.    if ( label )
  9.    {
  10. 	  std::cout << label << std::endl;
  11.    }
  12.    for ( citer it = alist.begin(), end = alist.end(); it < end; ++it )
  13.    {
  14. 	  std::cout << ' ' << *it << std::endl;
  15.    }
  16. }
  17. int main()
  18. {
  19.    // Make a list.
  20.    std::vector<std::string> mylist;
  21.    mylist.push_back("Phil");
  22.    mylist.push_back("Bob");
  23.    mylist.push_back("Fred");
  24.    // Show the list.
  25.    Show(mylist, "Before:");
  26.    // Sort the list.
  27.    std::sort(mylist.begin(), mylist.end());
  28.    // Show the list.
  29.    Show(mylist, "After:");
  30.    return 0;
  31. }
  32. /* my output
  33. Before:
  34.  Phil
  35.  Bob
  36.  Fred
  37. After:
  38.  Bob
  39.  Fred
  40.  Phil
  41. */
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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Re: sorting an array of string

 
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  #9
Jun 11th, 2004
hey,here a simple way to see which of 2 strings is greater

C Syntax (Toggle Plain Text) 
  1.  
  2. int str_alp(char *s1,char *s2)
  3. {
  4.     if(strcmp(s1,s2)==0)return(0);   //if they are equal
  5.  
  6.         for(int i=0;s1[i]!=0;i++)
  7.         {
  8.               if(s1[i] > s2[i])return(1);
  9.               else if(s1[i] < s2[i])return(2);
  10.         }
  11.  
  12.     return (2);  //hey if they are not equal and s1 not greater than s2 then s2 is greater
  13. }

See if you can use it
See what you can, remember what you need

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Re: sorting an array of string

 
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  #10
Jun 11th, 2004
>hey,here a simple way to see which of 2 strings is greater

Why not just check to see whether strcmp returns 1 (for greater than)? Or simply return the value returned by strcmp?
"One of the methods used by statists to destroy capitalism consists in establishing controls that tie a given industry hand and foot, making it unable to solve its problems, then declaring that freedom has failed and stronger controls are necessary." --Ayn Rand
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