whats going wrong with my program? - c

Question

the program is supposed to compare the strings and place them in alphabetical order, but the final printf statement prints garbage...where am i going wrong here?
i have used an array of pointers to strings and declared them in the begining, i have even tried using temp as an array rather than pointer stil doesnt quite work
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
int j;
int i;
char *temp;
char *string[5] = {"ibrahim","laura","peter","degea"};
for ( i = 0; i< 4;i++)
printf("%s\n", string[i]); //allocating memory
for( i = 0; i< 10 ;i++)
string[i] = (char*)malloc (30 * sizeof(char));
temp = (char*)malloc(30*sizeof(char));
for ( i=0; i< 3; i++)
for(j =i+1; j<4; j++)
{
if(strcmp(string[i], string[j]) > 0)
{
strcpy(temp, string[i]);
strcpy(string[i], string[j]);
strcpy(string[j], temp);
}
}
for (i = 0; i< 4; i++)
{
printf("%s\n",string[i]);
puts("\n");
}
free(string);
free(temp);
return 0;
}

Answer 1

string[i] = (char*)malloc (30 * sizeof(char));
This is overwriting the existing initialized values.
EDIT
for( i = 0; i< 10 ;i++)
temp = (char*)malloc(30*sizeof(char));
WHAT? you are allocating memory over and over 10 times on a single pointer?
EDIT 2:
The original post is lost (read Edited). By the time you are reading this answer, both Mr. Jonathan Leffler and this poster migh look like absolute fools in this world.

Answer 2

The code originally destroyed its data array (by allocating new pointers). Now it seems to throw memory away by allocating temp four times (but Jeevan's edit reinstates the old code in indented form). The old code allocated space for strings but never initialized them (having thrown away the value that was in the array beforehand).
NB: any commentary on the code could easily be invalid by the time you're reading the commentary — the code in the question could have changed.
for (i = 0; i < 10; i++)
string[i] = malloc(30);
This code tramples out of the bounds of the string array (dimension is 5). It also loses the data originally in the array.
You need to use strcmp() to compare the strings, but you simply need to swap pointers rather than using strcpy() at all.
The comment // allocating memory beside a printf() statement is misleading, too.
This stands a chance of working. Note that there is no memory allocation:
#include <stdio.h>
#include <string.h>
int main(void)
{
int j;
int i;
char *string[] = { "ibrahim", "laura", "peter", "degea" };
for (i = 0; i < 4; i++)
printf("%s\n", string[i]);
for (i = 0; i < 3; i++)
{
for (j = i+1; j < 4; j++)
{
if (strcmp(string[i], string[j]) > 0)
{
char *temp = string[i];
string[i] = string[j];
string[j] = temp;
}
}
}
for (i = 0; i < 4; i++)
printf("%s\n",string[i]);
return 0;
}
Output:
ibrahim
laura
peter
degea
degea
ibrahim
laura
peter
Comment: don't try sorting thousands of strings using this sort algorithm.

Answer 3

You are overwriting the existing string array contents with malloc, that too 10 times.
Please use braces in your code for better understanding
for( i = 0; i< 10 ;i++)
string[i] = (char*)malloc (30 * sizeof(char));
temp = (char*)malloc(30*sizeof(char));
can be written as
for( i = 0; i< 10 ;i++) // why to allocate memory ten times, that too overwriting
{
string[i] = (char*)malloc (30 * sizeof(char));
}
temp = (char*)malloc(30*sizeof(char));

Answer 4

when you declare :
char *string[5] = {
"ibrahim",
"laura",
"peter",
"degea" };
the pointer *string[0] to *string[3] allocated to a address in the memory, where will stored the init values "ibrahim","laura"...
when you use malloc function for the pointer string[i] = (char*)malloc (30 * sizeof(char));
the pointer *string[0] to *string[4] will be allocated to another address in the memory. so the value at these address are different from that you initialized (ibrahim,laura).
you should use static array instead dynamic as below
char temp;
char string[5] = {
"ibrahim",
"laura",
"peter",
"degea" };
remove all the malloc, free function.