c语言程序实现大小写的转换，小白求帮忙找错误........真心搞不懂

#include#includevoid main(){char a1,a2;scanf("%c",&a1);if (a1>='A'&&a1='a'&&a1<='z'){ a2=a1-32; printf("a2=%c\n",a2);}else printf("WRONG! Please enter again!\n"); system("pause"