Reversing a string in C using loop [duplicate] - c

Question

This question already has answers here:
Function to reverse string in C
(4 answers)
Closed 6 years ago.
Beginner programmer here. I'm trying to take an input from user, reverse it and show the result. For some reason, it's printing blanks instead of the reversed string. I know that array[i] has the right information because if I use this loop on line for (int i=0; i<count; i++), it's printing the right characters. It's just not printing in reverse. What am I not getting here?
#include <stdio.h>
#include <cs50.h>
#include <string.h>
int main(void)
{
printf("Please enter a word: ");
char *word = get_string();
int count = strlen(word);
char array[count];
for (int i=0; i< count; i++)
{
array[i] = word[i];
}
for (int i=count-1; i==0; i--)
{
printf("%c ", array[i]);
}
printf("\n");
}

Answer 1

for (int i=0; i< count; i++)
{
array[i] = word[i];
}
You go over the string and copy it, you do not reverse it.
There is also a subtle bug in-waiting in your declaration of array, since you do not leave space for the '\0' character terminator. Passing your buffer to printf as a C-string, as opposed to character by character will have undefined behavior.
So to fix those two particular errors:
char array[count + 1];
array[count] = '\0';
for (int i = 0; i< count; i++)
{
array[i] = word[count - i];
}
As a side note, it may not mean much to use a VLA for this small exercise, but for larger inputs it could very well overflow the call stack. Beware.

Answer 2

// the header where strlen is
#include <string.h>
/**
* \brief reverse the string pointed by str
**/
void reverseString(char* str) {
int len = strlen(str);
// the pointer for the left and right character
char* pl = str;
char* pr = str+len-1;
// iterate to the middle of the string from left and right (len>>1 == len/2)
for(int i = len>>1; i; --i, ++pl, --pr) {
// swap the left and right character
char l = *pl;
*pl = *pr;
*pr = l;
};
};
And just call the function:
int main(void) {
printf("Please enter a word: ");
char *word = get_string();
// Just call the function. Note: the memory is changed, if you want to have the original and the reversed just use a buffer and copy it with srcpy before the call
reverseString(word)
printf("%s\n", word);
};
And just change
char array[count];
for (int i=0; i< count; i++)
{
array[i] = word[i];
}
to
// add an other byte for the null-terminating character!!!
char array[count+1];
strcpy(array, word);