C program to reverse the string word by word

The following C program will reverse the string word by word
Example:
If the input is : Have a nice day
Output will be:day nice a Have

#include 
#include 

void swap(char *string, int length)
{
 int i;
 char ch; 
 for (i = 0; i < length/2; i++)
 {
  ch = string[length-i-1];
  string[length-1-i]=string[i];
  string[i]=ch;
 }

}

char *reverse(char *string)
{

 int length = strlen(string);
 char ch;
 int i, prev_index;

 /*
  *  The following for loop for swap the character to character
  */
 for ( i = 0 ; i < length/2; i++)
 {
  ch = string[length-1-i];
  string[length-1-i] = string[i];
  string[i] = ch;
 }
 /*
  * Next for loop we have to swap word by word
  */
 i = 0;
 while (string[i] !='\0')
 {
  prev_index = i;
  while (string[i] != ' ' && string[i] != '\0')
   i++;
  swap(string+prev_index,i - prev_index);
  if(string[i] == ' ')
   i++;

 }
 return string;
}


int main(int argc, char *argv[])
{

 char str[100];

 printf("Enter the string:\n");
 scanf("%[^\n]",str);
 printf("string before reverse:%s\n",str);
 printf("string in reverse order:%s\n",reverse(str));

}