> 各位牛人，有谁用c做出来的，用到栈的，贴一下代码，我参考一下，这里谢谢了。
#include <stdio.h>
#include <string.h>

char backward[101][100];
char forward[101][100];
int cback,cfor;

int main()
{
	char command[100],url[100],curr[100]="http://www.acm.org/";
	while(scanf("%s",command)!=EOF)
	{
		if(!strcmp(command,"QUIT"))break;
		else if(!strcmp(command,"BACK"))
		{
			if(cback==0)
			{
				printf("Ignored\n");
				continue;
			}
			strcpy(forward[cfor++],curr);
			strcpy(curr,backward[--cback]);
			printf("%s\n",curr);
		}
		else if(!strcmp(command,"FORWARD"))
		{
			if(cfor==0)
			{
				printf("Ignored\n");
				continue;
			}
			strcpy(backward[cback++],curr);
			strcpy(curr,forward[--cfor]);
			printf("%s\n",curr);
		}
		else if(!strcmp(command,"VISIT"))
		{
			scanf("%s",url);
			strcpy(backward[cback++],curr);
			strcpy(curr,url);
			cfor=0;
			printf("%s\n",curr);
		}
	}
	return 0;
}