keil4 undefined identifier 整不会了

Question

#include "Delay.h"
#include "MatrixKey.h"
#include "NixieTube.h"

 	unsigned char keyNum;
	void main()
	{
	   while(1)
	   {
	   		keyNum=scanKeyByColumn();
			if(keyNum>10)
			{
			   	char ge=keyNum%10;
		    	char shi=(keyNum/10)%10;
				nixieTube(1,shi,0);
				nixieTube(2,ge,0);
			}
		
		
		
	   }
	
	}

51单片机扫描矩阵键盘,将对应的数字送到数码管显示,上面的写法编译没问题,可是我把if删掉,像下面这种写法就会编译出错

#include "Delay.h"
#include "MatrixKey.h"
#include "NixieTube.h"

 	unsigned char keyNum;
	void main()
	{
	   while(1)
	   {
	   		keyNum=scanKeyByColumn();
			char ge=keyNum%10;
		    char shi=(keyNum/10)%10;
			nixieTube(1,shi,0);
			nixieTube(2,ge,0);
	   }
	
	}

显示变量未定义,使用软件为keil4

Answer 1

先声明再使用就没问题了,为什么不能声明的同时直接初始化?