My try inspired by bitingduck's triple reverse:

#include <stdio.h>
#include <string.h>

void reverse( char*p, int n ) {
    char c, *e = p+n-1;

    n /= 2;
    while( n-- ) c = *p, *p++ = *e, *e-- = c;
}

char *reverseWords( char*line ) {
    int len = (int)strlen( line );
    char *p = line, *p1 = line, *e = line+len;

    reverse( line, len );

    while( p <= e ) {
        if( *p == 32 || *p == 0 ) {
            reverse( p1, (int)( p - p1) );
            p1 = p+1;
        }
        ++p;
    }
    return line;
}

int main( int argc, char **argv ) {
    char line[ 1024 ];
    printf( "%s\n", reverseWords( gets_s( line, 1024 ) ) );
    return 0;
}
[download]