Reverse string(Swaping) - c

Question

I need help about this exam.I need to reverse the input string.
int main(void)
{
char str[30];
int strlen; int i=0; int count=0;int temp;int j;
printf("Enter the string \n");
gets(str);
while(str[i]!='\0')
{
i++;
count++;
}
strlen=count;
printf("The length of the string:%d\n", strlen);
i=0;
j=strlen;
while(i<j)
{
temp=str[i];
str[i]=str[j];
str[j]=temp;
i++;
j--;
}
printf("Reverse string :%s",str);
return 0;
}
The problem is that at the end its not show me the string.
It shows me :
"Reverse string :"
and that is, no reverse string. Where is my mistake?

Answer 1

In your code you are doing
j=strlen;
j points to the last index of the string which will be '\0'
And later in the loop you set str[i]=str[j];
Therefore, the first index will be \0
Printing str will display nothing
In order to make the code correct set j=strlen - 1;

Answer 2

Try this:-
As In your code you are assigning j=strlen pointing to \0 or null character change it to j=strlen-1;
char str[30];
int strlen;int i=0;int count=0;int temp;int j;
printf("Enter the string \n");
gets(str);
while(str[i]!='\0')
{
i++;
count++;
}
strlen=count;
printf("The lenht of the string:%d\n",strlen);
i=0;
j=strlen-1;
while(i<j)
{
temp=str[i];
str[i]=str[j];
str[j]=temp;
i++;
j--;
}
printf("Reverse string :%s",str);

Answer 3

The problem is with the assignment j=strlen;'.
People will suggest you to change it toj=strlen - 1;`
But, I'll recommend to resolve at its root.
while(str[i]!='\0')
{
i++;
count++;
}
After this loop, count will hold value as the index which has a '\0' of the string. Here, you should decrement count and then assign it to strlen. That makes the code more understandable.
With this change, you'll also have to change
printf("The length of the string: %d\n", strlen);
to
printf("The length of the string: %d\n", strlen+1);
as it would print
The length of the string: 4
instead of 5 for "Hello" because of the decrement.
Additionally, strlen is a function once you include string.h header file in your code. To keep it portable, you should always use naming convention which won't have standard, common function names (such as strlen) as a variable name in your code.
A slightly better version (using purely your logic) than your existing code will use one variable less, and will look like this:
#include<stdio.h>
int main(void)
{
//char str[30] = "Hello";
char str[30] = { [0 ... 29] = 0 };
//int str_length = 0;
int i = 0, count = 0, j = 0;
char temp = 0; //This should be a char rather than an int
printf("Enter the string \n");
gets(str);
while(str[i]!='\0')
{
i++;
count++;
}
printf("The length of the string: %d\n", count);
if(count) count--;
//str_length = count;
i = 0;
j = count;
while(i < j)
{
temp=str[i];
str[i]=str[j];
str[j]=temp;
i++;
j--;
}
printf("Reverse string :%s", str);
return 0;
}