C - Reverse order of words in an array of Strings - c

Question

I did this program to reverse the order of the words in the give string. (And it works)
i.e. Output: sentence first the is This
However I am stuck when it comes to adding another sentence to the array.
For example I need to have an array {"This is the first sentence", "And this is the second"} producing as output: sentence first the is This , second the is this And
int main() {
char str[] = {"This is the first sentence"};
int length = strlen(str);
// Traverse string from end
int i;
for (i = length - 1; i >= 0; i--) {
if (str[i] == ' ') {
// putting the NULL character at the position of space characters for
next iteration.
str[i] = '\0';
// Start from next character
printf("%s ", &(str[i]) + 1);
}
}
// printing the last word
printf("%s", str);
return 0;
}
I am new to C so its not surprising that I got stuck even if the solution is quite easy. Any help would be appreciated! Thanks!

Answer 1

Since you already have the code to print the words of one string in reverse order, I would suggest making that a function which takes a single string as an argument, i.e.:
void print_words_reverse(char * const str) {
// your current code here
}
Then you can call it separately for each string:
char strings[][30] = {
"This is the first sentence",
"And this is the second"
};
for (int i = 0; i < sizeof(strings) / sizeof(*strings); ++i) {
print_words_reverse(strings[i]);
}
Note that since you are modifying the string (by replacing spaces with NUL bytes), the argument needs to be modifiable, which means you are not allowed to call it (in standard C) with a pointer to a string literal, which means you can't simply use const char *strings[] = { "first", "second" }. You could get rid of the ugly constant length (here 30) reserved for every string by making your code not modify the argument string. Or you could have a separate char array for each sentence and then use pointers to those (modifiable) strings.

Answer 2

First, you can try with a two-dimensional array or use an array of pointers.
Secondly, in your approach, you lose the initial value of your string, I don't know how important it is.
This is my fast approach using arrray of pointers.
#include <stdio.h>
#include <string.h>
static void print_word(const char *str)
{
for (int i = 0; str[i] && str[i] != ' '; i++)
printf("%c", str[i]);
putchar(' ');
}
int main(void)
{
int len;
const char *str[] = {"This is the first sentence",
"And this is second", NULL};
for (int i = 0; str[i]; i++) {
for (len = strlen(str[i]); len >= 0; len--) {
if (len == 0)
print_word(&str[i][len]);
else if (str[i][len] == ' ')
print_word(&str[i][len + 1]);
}
putchar('\n');
}
printf("Initial value of array of strings [%s | %s] \n", str[0], str[1]);
return 0;
}
output is:
sentence first the is This
second is this And
Initial value of array of strings [This is the first sentence | And this is second]

Answer 3

I suggest you using memcpy but without altering too much your code this seems to work
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define MAX_STRING_LENGTH 100
int main()
{
char *str[] = {"This is the first", "And this is the second sentence"};
const size_t NUM_STRING = sizeof(str)/sizeof(char*);
/*%z used to print size_t variables*/
printf("%zd strings found\n", NUM_STRING);
int length[2];
int i;
for (i=0; i<NUM_STRING; i++)
{
length[i] = strlen(str[i]);
}
printf("length initialized %d %d\n", length[0], length[1]);
// Traverse string from end
int j = 0;
char temp[MAX_STRING_LENGTH];
printf("\n\n");
for (j=0; j<NUM_STRING; j++)
{
/*Make sure the string respect the MAX_STRING_LENGTH limit*/
if (strlen(str[j])>MAX_STRING_LENGTH)
{
printf("ERROR: string %d exceding max string length %d defined in constant "
"MAX_STRING_LENGTH. Exiting from program.\n", j, MAX_STRING_LENGTH);
exit(1);
}
//reset temporary string
memset(temp, '\0', sizeof(temp));
//printf("temp variable reinitialized\n");
for (i = length[j] - 1; i >= 0; i--)
{
temp[i] = str[j][i];
if (str[j][i] == ' ')
{
// putting the NULL character at the position of space characters for next iteration.
temp[i] = '\0';
// Start from next character
printf("%s ", &(temp[i]) + 1);
}
}
// printing the last word
printf("%s ", temp);
}
printf("\n");
return 0;
}