String substitution

This question requires the preparation of procedures , Replace the uppercase letters in the given string according to the following corresponding rules ：

Original letter	The corresponding letters
A	Z
B	Y
C	X
D	W
…	…
X	C
Y	B
Z	A

Input format ：

The input gives no more than 80 Characters 、 A string that ends with a carriage return .

Output format ：

The output gives the string after replacement in one line .

sample input ：

Only the 11 CAPItaL LeTtERS are replaced.

sample output ：

Lnly the 11 XZKRtaO OeGtVIH are replaced.

Code ：

#include <stdio.h>
int main(){
    char a[26],b[80],c[26];
    int i,j,num;
    for(i=0;(b[i]=getchar())!='\n';i++);
    num=i;
    for(i=0;i<=25;i++){
        a[i]='Z'-i;
        c[i]='A'+i;
    }
    for(i=0;i<num;i++){
        if(b[i]>='A'&&b[i]<='Z'){
        for(j=0;j<=25;j++){
            if(b[i]==c[j])printf("%c",a[j]);
        }
        }
        else {
        	printf("%c",b[i]);
		} 
    }
}