7-4 replacement string (15 minutes)

7-4 replacement string (15 points)
This problem requires programming, given the string of capital letters corresponding to the following replacement rule:

Original letter in the letter
AZ
BY
the CX
DW
... ...
XC
YB
ZA
input format:
Enter a given line does not exceed 80 characters, carriage return and the end of the string.

Output format:
replacement string given output row is completed.

Sample input:
Only The Capital Letters. 11 are REPLACED.
Output Sample:
Lnly The XZKRtaO OeGtVIH are REPLACED. 11.

#include<iostream>
#include<cmath>
#include<cstring>
using namespace std;

int main()
{
    char b[81];
    char a[]={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
    int i=0,c;

    cin.getline(b,81);
    c=strlen(b);
    for(i=0;i<c;i++)
    {
        for(int j=0;j<=25;j++)
        {
            if(b[i]==a[j])
            {
                b[i]=a[25-j];
                break;
            }
        }
    }
    
    for(int i=0;i<c;i++)
    cout<<b[i];
    

   
    return 0;
}