Program in C to reverse the words

Write a program in C to reverse the words

#include <stdio.h>

#include <conio.h>

#include <string.h>

const int opt = 50;

int main()

{

          int i=0,j=0,c=0,vali[opt] = {0};

          char str1[opt],str2[opt]="",str3[opt]="",ch;

          printf("please enter your sentence :");

          gets(str1);

          for(i=0;str1[i] != '\0';i++)

          {

                   if(str1[i] == ' ')

                   {

                             vali[j+1] = i;

                             j++;

                   }

          }

          c = j;

          for(i=0;i<=j && c!=0;i++)

          {

                   strcat(str2,&str1[vali[c]+1]);

                   strcpy(&str1[vali[c]],str3);

                   strcat(str2," ");

                   c--;

          }

          strcat(str2,str1);

          printf("\nyour reversed sentence is :");

          puts(str2);

          getch();

          return 0;

}