Program to reverse the order of words in a string

Program to reverse the order of words in a string.
For Eg:
Input: this is a simple c program
Output: program c simple a is this

The LOGIC part:
-First determine the length of the string. Use a simple for loop
until you find '\0' else use an inbuilt string function 'strlen()' like I have used.
-then move over to the last word in your string.
Place a pointer at the end of the last word and then find the
space before that word and place a pointer after the space
and using these two pointer append the word to a new string.
-Repeat procedure for all words from last word to first word.


SOURCE CODE:

 #include <stdio.h>  
 #include <stdlib.h>  
 int main()  
 {  
      char str[100], rev[100];  
      int i, j, k, m, n, len, c=0, flag=1;  
      printf("\nEnter a sentence: ");  
      gets(str);  
      printf("\nEntered sentence: ");  
      puts(str);  
      len = strlen(str)-1;          //length of string except \0  
      i=0;  
      j=len;  
      k=0;  
      while(flag==1)                    //while more words to process  
      {  
           flag = 1;  
           i=j;                         //pointer i, j to end of current word  
           while(str[i] != ' ')     //decrement pointer i till beginning of current word  
           {  
                if(i==0)  
                {  
                     flag = 0;          //special case for 1st word of the sentence  
                     break;  
                }  
                i--;  
           }  
            m=i;  
           if(flag)  
           {  
                i=i+1;       
           }       
           for( ; i<=j; )               //append current word to new char array  
           {  
                rev[k++] = str[i++];  
           }  
           j=m-1;                         //move pointer j to end of previous word  
           rev[k++]=' ';  
      }  
      rev[k]='\0';  
      printf("\nReverse sentence: ");  
      puts(rev);  
      printf("\n");  
      return 1;  
 }  

SAMPLE OUTPUT: