Problems with creating a function to reverse a string [closed] - c

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I need to create a fuction that returns a string. So far I have come up with this code:
#include <stdio.h>
#include <string.h>
#define SIZE 256
void str_reverse(char[SIZE], char[SIZE]);
int main(void)
{
char input[SIZE];
char output[SIZE];
printf("Please enter a string\n");
fgets(input, SIZE, stdin);
str_reverse(input, output);
printf("%s \n", output);
return 0;
}
void str_reverse(char in[SIZE], char out[SIZE])
{
int i = strlen(in);
int k = 0;
for(int j = i; j>= 0; j--)
{
out[k] = in[j];
k++;
}
}
However, whenever I try to run the code, I do not get an output. Does anyone have any idea what could be wrong

Answer 1

The problem is this line
int i = strlen(in);
Change it to
int i = strlen(in)-1;
strlen() returns the size of the string, hence when you start copying from in[], in[j] would be \0. which is getting stored in out[0].
Another change you need to do is put a \0 in the out[], just after the for loop
for(int j = i; j>= 0; j--)
{
out[k] = in[j];
k++;
}
out[k] = '\0';

Answer 2

Your "reversing" includes the null character too. So the reversed string's first character is '\0'. So the string is empty.
Change:
for(int j = i ; j>= 0; j--)
to
for(int j = i - 1; j>= 0; j--)
You should also check if the string length is zero before the for loop. Otherwise, i-1 will become SIZE_MAX and you'll have problems with that!
A simple condition such as the following in str_reverse() would handle that case:
size_t i = strlen(in);
int k = 0;
if (i<=1) return; //empty string or contains only 1 char char.

Answer 3

i starts out at strlen(in), so the first character you copy over tooutis the null byte at the end of the string. Every other character then appears after the null terminator, soout` is an empty string.
Start with i at strlen(in) - 1, then add the null terminator and the end of the loop:
int i = strlen(in) - 1; // start at the last non-null character
int k = 0;
for(int j = i; j>= 0; j--)
{
out[k] = in[j];
k++;
}
out[k] = '\0'; // add the null terminator

Answer 4

When k is 0 and j is i, you do the following:
out[0] = '\0';
Hence, out looks like an empty string when the function returns.
Use:
for(int j = i-1; j>= 0; j--)
{
out[k] = in[j];
k++;
}
out[k] = '\0';

Answer 5

In the function variable i is set the following way
int i = strlen(in);
So within the loop
for(int j = i; j>= 0; j--)
{
out[k] = in[j];
k++;
}
then j is equal to i then in[j] is equal to the terminating zero '\0' of string in. Thus array out starts from zero that is it will contain an empty string.
It is better to declare the function itself the following way
char * str_reverse( char *out, const char *in );
and to return from the function the pointer out. In this case you could write for example
puts( str_reverse( output, input ) );
Take into acount that function fgets usually also stores the new line character in the string. You should remove it. you can do it the following way
input[strcspn( input, "\n" )] = '\0';
Also instead of the type int in this statement
int i = strlen(in);
it is better to use type size_t.
size_t i = strlen(in);
It is the type of the return value of the function strlen. But in this case you should also to write the loop correctly.:)