实现isalpha的功能

#include <stdio.h>int isletter(int input){input=getchar();if(input>='a'&&input<='z'||input>='A'&&input<='Z'){return 0;}return -1;}int main(){int c;scanf("%d",&c);if(isletter(c)==0){printf("is a letter\n");}else{printf("isn't a letter\n"); }}