ABCD123efgh
abcd123EFGH
#include<stdio.h> #include<string.h> int main() { char a[100]; int len,i; gets(a); for(i=0;a[i]!='\0';i++) { if(a[i]>='A'&&a[i]<='Z') a[i]=a[i]+32; else if(a[i]>='a'&&a[i]<='z')//else很重要// a[i]=a[i]-32; } puts(a); return 0; }