Reverse string function not working properly - c

Question

Here is my code. I just can't seem to figure it out. Sometimes i get no output, and sometimes i just get 3 random characters, regardless of how long the entered string is.
#include <stdio.h>
#include <math.h>
#include <string.h>
void reverse(char* array, int numberOfChars);
int main()
{
char string[250];
int length;
printf("Enter a string: ");
gets(string);
printf("How long is the string:");
scanf("%d", &length);
reverse(string, length);
printf("Reversed string is: %s\n"), string;
return 0;
}
void reverse(char *userArray, int numberOfChars)
{
char temp;
int fromEnd = 0, fromStart = 0;
fromEnd = numberOfChars;
while (fromStart < fromEnd)
{
temp = userArray[fromStart];
userArray[fromStart] = userArray[fromEnd];
userArray[fromEnd] = temp;
fromStart++;
fromEnd--;
}
}
I really dread asking these questions here but I can't seem to fix it...
Any help appreciated

Answer 1

Conceptually you need to swap the ends until you are left with a string of length 0 or 1. You don't need to test for the length of the remaining portion of the string after each iteration however, because it can be shown that exactly length/2 swaps will be needed.
void reverse (char *s)
{
size_t length = strlen (s);
for (size_t i = 0; i < length / 2; i++) {
char tmp;
tmp = s[i];
s[i] = s[length - 1 - i];
s[length - 1 - i] = tmp;
}
}

Answer 2

There is no need to complicate things like that, try this:
#include <stdio.h>
int main(void){
char *src = "Michi";
char dest[256];
int i=-1,j=0;
while(src[++i]!='\0');
while(i>=0){
dest[j++] = src[--i];
}
dest[j]='\0';
printf("Your new string is: %s",dest);
return 0;
}
Output:
Your new string is: ihciM
This is probably what you need:
#include<stdio.h>
#include<string.h>
void reverse(char *ptr);
int main(void) {
char src[256] = "Michi";
reverse(src);
printf("Your new string is: %s",src);
return (0);
}
void reverse(char *src){
char dest;
size_t i, j = 0;
i = 0;
j = strlen(src) - 1;
while (i < j) {
dest = src[i];
src[i] = src[j];
src[j] = dest;
i++;
j--;
}
}

Answer 3

don't use gets(),use fgets().To reverse strings,you don't need to pass number of characters,since strings in C are null-terminated.check this very simple function:
#include <stdio.h>
void reverse(char *_Str);
int main(void)
{
char str[] = "Hello Buddy";
reverse(str);
printf("%s\n",str);
return 0;
}
void reverse(char *_Str)
{
char tmp,*_b,*_e;
_b = _e = _Str;
while(*_e) _e++;
_e--;
while(_b < _e)
{
tmp = *_b;
*_b++ = *_e;
*_e-- = tmp;
}
}

Answer 4

Well the very important line you missed is assigning the null character. And do not take the length of your string as an input from the user. use the function some_integer=strlen(stringname); This will return the length of your stringname and assign it to some_integer. Your function to reverse the string should be as
void reverse(char *userarray) // no need of a second argument. Do not trust your users.
{
char temp;
int fromEnd,fromStart = 0; /
fromEnd = strlen(userarray)-1; // here the length of your string is assigned to fromEnd.
while (fromStart < fromEnd)
{
temp = userArray[fromStart];
userArray[fromStart] = userArray[fromEnd];
userArray[fromEnd] = temp;
fromStart++;
fromEnd--;
}
userarray[strlen(userarray)-1]='\0'; //You missed this line (very important)
}
And chek your printf statement.
It should be
printf("Your reversed string is %s \n",string);
not
printf("Your reversed string is %s \n"),string;
I belive this will work. Check it and let me know if it works for you.

Answer 5

Incorrect code. The needed string for the printf() is not in the function. #M Oehm
/// printf("Reversed string is: %s\n"), string;
printf("Reversed string is: %s\n", string);
Also original code can easily wipe out the string terminating null character '\0'. Better to use strlen(string) rather than ask the user for the length.
Likely should use - 1 as commented by #WalterM. It is unclear what values OP is using.
// fromEnd = numberOfChars;
if (numberOfChars <= 0) return;
fromEnd = numberOfChars - 1;
Answers I have seen so far depend on int well addressing all elements of a string. size_t is the right approach as int may be too small.
Many answers would fail on a string such as "".
So here is another contribution without those restrictions.
#include <string.h>
#include <stdio.h>
char *str_revese_inplace(char *s) {
char *left = s;
char *right = s + strlen(s);
while (right > left) {
right--;
char t = *right;
*right = *left;
*left = t;
left++;
}
return s;
}
void stest(const char *s) {
char t[strlen(s) + 1];
// or char t[100];
strcpy(t, s);
printf("'%s' --> '%s'\n", s, str_revese_inplace(t));
}
int main(void) {
stest("123");
stest("12");
stest("1");
stest("");
return 0;
}
Output
'123' --> '321'
'12' --> '21'
'1' --> '1'
'' --> ''