sortstrings.c

/*
* This code accepts strings from the user.
* It then sorts them, prints the sorted output.
*/

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

bool str_in(char **,int *);	/* function prototype for string input */
void str_sort(const char *[], int);	/* function prototype for string sort */
void swap(const char **p1, const char **p2);	/* swap two pointers */
void str_out(char *[], int);	/* function prototype for string output */

const size_t BUFFER_LEN = 256;	/* Max length for each string */
const size_t NUM_P = 50;	/* Max number of strings */

/*
* main function
*/
int main(){
	int numofstr = 0;
	char **arrayofstr = NULL;
	arrayofstr = (char **)malloc(sizeof(char *)*NUM_P);	/* Allocating an array
																 of char * */
	if(arrayofstr==NULL){
		printf("main: Error while allocating memory. Exiting now!");
    	exit(1);
	}
	while(str_in(arrayofstr,&numofstr));	/* Calls function to accept strings
																 from user */
	str_sort(arrayofstr,numofstr);
	str_out(arrayofstr,numofstr);
}

/*
* 	String input routine
* @arrayofstr array of strings where the string will be stored
* @numofstr number of strings entered so far
* Returns: true, when user enters a valid string,
* and false, otherwise. 
* If no memory is obtained, or if there is an 
* error reading from the keyboard, the program is
* terminated by calling exit()
*/
bool str_in(char ** arrayofstr, int *numofstr){
	bool ret = true;
	int index = 0;
	char *str = NULL;
	str = (char *)malloc(sizeof(char)*BUFFER_LEN);	/* Allocate memory for the
															 input string */
	if(!str){
		printf("str_in: Error while allocating memory. Exiting now!");
		exit(1);
	}
	for(index=0;index<NUM_P;index++){	/* Store the allocated block of memory
														 in a char** array */
		if(*arrayofstr==NULL){
			*arrayofstr = str;
			*numofstr = index+1;
			break;
		}else{
			arrayofstr++;
		}
	}
	index=0;
	while((*str++=getchar())!='\n' && index++ < (BUFFER_LEN-1));	/* Accept 
																user input */
	if(index==0){
		*numofstr -= 1;
		return false;	/* user entered a just new line character indicating
															 end of input */
	}else{
		*str='\0';	/* add an ending null char to the string */
		return true;
	}
}

/*
*	String output routine
* @arrayofstr array of strings to be displayed
* @count number of strings in the array
* Return: void
*/
void str_out(char * arrayofstr[], int count){
	int index=0;
	for(index=0;index<count && index<NUM_P;index++){
		printf("%s\n",arrayofstr[index]);
	}
}

/*
*	Sort the strings
* @arrayofstr Array containing the strings
* @numofstr number of strings
* Sorts the array of strings, using bubblesort
*/
void str_sort(const char * arrayofstr[], int numofstr){
	int index = 0;
	int index2 = 0;
	for(index=0;index<numofstr;index++){
		for(index2=index+1;index2<numofstr;index2++){
			if(strcmp(arrayofstr[index],arrayofstr[index2]) > 0){
				swap(arrayofstr+index,arrayofstr+index2);
			}
		}
	}
}

/*
*	Swap the strings
* @p1 pointer to pointer to first string. the string itself is constant
* @p2 pointer to pointer to second string. the string itself is constant
* Swaps the strings
*/

void swap(const char **p1, const char **p2){
	char *tmp = NULL;
	tmp=(char *)*p1;
	*p1=*p2;
	*p2=tmp;
}