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

void strip_newline( char *str, int size )
{
    int i;
    for (  i = 0; i < size; ++i )
    {
        if ( str[i] == '\n' )
        {
            str[i] = '\0';
            return;   
        }
    }
}

int main()
{	
	char input[100];
	char output[100];
	printf("Nhap input string: ");
	fgets(input, 100, stdin);
	// Loai new line o ngay truoc null character khoi input string
	strip_newline(input, strlen(input));
	// review input string
	printf("Review input string: %s", input);
	// Chuan bi san sang cho output string
	*output = '\0';
	// Duyet nguoc input string:
	int index;	
	for(index=strlen(input)-1; index >=0; index--)
	{
		if(*(input+index) == 0x20){
			// Noi doan substring sau blank space vao output string
			strcat(output, input + index + 1);
			// Them ky tu 0x20 vao ngay truoc ky tu NULL cua output string
			*(output + strlen(output)) = 0x20;
			*(output + strlen(output) + 1) = '\0';
			// Thu gon lai input string
			*(input+index) = '\0';
		}
	}
	// Ra khoi vong lap, van con sot mot tu trong do, noi not vao output string
	strcat(output, input);
        // Cho input string chua null char o dau, coi nhu la da chuyen het tu trong input string sang output string
	*input = '\0';

	//Hien thi ket qua
	printf("\n========================");
	printf("\nOutput string: %s", output);
	printf("\n");

	getchar();	
	return 0;
}

*(output + strlen(output) + 1) = '\0';

Restring.c:39:35: warning: assignment makes integer from pointer without a cast