Reverse every word in a string (should handle space) - c++

Question

Examples:
char test1[] = " ";
char test2[] = " hello z";
char test3[] = "hello world ";
char test4[] = "x y z ";
Results:
" "
" olleh z"
"olleh dlrow "
"x y z "
The problem:
Reverse every world in a string, ignore the spaces.
The following is my code. The basic idea is to scan the string, when
finding a word, then reverse it. The complexity of the algorithm is
O(n), where n is the length of the string.
How do verify it? Is there a better solution?
void reverse_word(char* s, char* e)
{
while (s < e)
{
char tmp = *s;
*s = *e;
*e = tmp;
++s;
--e;
}
}
char* word_start_index(char* p)
{
while ((*p != '\0') && (*p == ' '))
{
++p;
}
if (*p == '\0')
return NULL;
else
return p;
}
char* word_end_index(char* p)
{
while ((*p != '\0') && (*p != ' '))
{
++p;
}
return p-1;
}
void reverse_string(char* s)
{
char* s_w = NULL;
char* e_w = NULL;
char* runner = s;
while (*runner != '\0')
{
char* cur_word_s = word_start_index(runner);
if (cur_word_s == NULL)
break;
char* cur_word_e = word_end_index(cur_word_s);
reverse_word(cur_word_s, cur_word_e);
runner = cur_word_e+1;
}
}

Answer 1

Your code seems correct, but it's plain C. In C++, using the same approach, it could look something like this:
#include <iostream>
#include <string>
#include <iterator>
#include <algorithm>
#include <cctype>
int main()
{
std::string str = " cat cow dog wolf lobster";
std::string result;
auto it = str.begin();
while (it != str.end()) {
while (it != str.end() && isspace(*it)) {
result += *it;
++it;
}
auto begin = it;
while (it != str.end() && !isspace(*it)) {
++it;
}
auto end = it;
result.append(std::reverse_iterator<decltype(end)>(end),
std::reverse_iterator<decltype(begin)>(begin));
// if you want to modify original string instead, just do this:
std::reverse(begin, end);
}
std::cout << result <<'\n';
}

Answer 2

In-place, ANSI C89.
#include <ctype.h>
#include <stdio.h>
void reverse(char *s) {
int i = 0, j, k;
while (1) {
while (isspace(s[i])) i++;
if (!s[i]) return;
for (j = i; !isspace(s[j]) && s[j] != '\0'; j++);
for (k = 0; k < (j - i) / 2; k++) {
char t = s[i + k];
s[i + k] = s[j - k - 1];
s[j - k - 1] = t;
}
i = j;
}
}
int main(int argc, char**argv) {
if (argc != 2) return 1;
reverse(argv[1]);
printf("%s\n", argv[1]);
return 0;
}

Answer 3

#include<iostream>
#include<string.h>
using namespace std;
int main()
{
char s[89];
cout << "enter\n";
gets(s);
int k;
int p = strlen(s);
strcat(s," ");
for(int i=0; i <= p; i++)
{
if(s[i]==' ')
{
for (k = i-1; (k != -1) && (s[k] != ' '); k--)
cout<<s[k];
cout<<" ";
}
}
return 0;
}

Answer 4

#include<iostream>
#include<cstring>
using namespace std;
int main()
{
char str[100],a[10],s[100]=" ";
int i,j;
cout<<"enter a string";
cin.getline(str,100);
strcat(s,str);
for(i=0;s[i]!='\0';i++)
{
if(s[i]==' '&&s[i+1]!=' '&&s[i+1]!='\0')
{
cout<<" ";
if(i==0)cout<<"\b";
j=i+1;
while(s[j]!=' '&&s[j]!='\0')
{
j++;
}
j--;
while(s[j]!=' ')
{
cout<<s[j];
j--;
}
}
else if(s[i]==' ')
{
cout<<" ";
if(i==0)cout<<"\b";
}
}
return 0;
}

Answer 5

#include <iostream>
#include<string.h>
#include<stdio.h>
using namespace std;
void Reverse_Each(char st[60])
{
int i,j,k=0,p=0,l;
char sr[60];
l=strlen(st);
for(i=0;i<=l;i++) {
if((st[i]==' ')||(st[i]=='\0')) {
for(j=i-1;j>=p;j--) {
sr[k]=st[j]; k++;
}
sr[k]=' '; k++; p=i+1;}
}
for(i=0;i<p;i++)
cout<<sr[i];
}
int main(){
char s[60];
gets(s);
Reverse_Each(s);
return 0;
}