为什么全部re

#include<stdio.h>
int main(void){
    int n,i=0,b;
    scanf("%d",&n);
    char a[55],ch;
    getchar();
    scanf("%c",&ch);
    while(ch!='\n'){
        a[i]=ch;
        i++;
        scanf("%c",&ch);
    }
    for(b=0;b<i;b++){
        if(a[b]<=122-n) a[b]=a[b]+n;
        else a[b]=a[b]+n-26;
        printf("%c",a[b]);
    }
    return 0;
}