14.if条件判断语句（中）
set name  age 



if 3 equ 3 (echo equal) else (echo not equal)
判断是否相等 

@echo off
set num1=1
set num2=2
if  %num1% equ %num2% (echo equal) else (echo not equal)
pause >nul


@echo off
set /p num1=请输入数字1：
set /p num2=请输入数字2：
if  %num1% equ %num2% (echo equal) else (echo not equal)
pause >nul


判断某个变量是否已经被赋值，用if defined str 语句

查看是否被赋值

@echo off
if defined name (echo yes) else (echo not)
pause >nul