#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
 
int main(int argc, char *argv[])
{
    char a[100] = "Payment is COD Upon Arrival Or Cash Discount Applies";
    char b[100] = "", *pa=a, *pb=b;
    int ar[1 << CHAR_BIT];
    int i=0;
 
    // prep table.
    for (;i<sizeof(ar)/sizeof(ar[0]);++i)
        ar[i] = i;
 
    // load translations
    ar['C'] = 'b';
    ar['O'] = 'a';
    ar['D'] = 'l';
 
    // TODO: load string b
 
    // do xlat
    while (*pa)
        *pb++ = ar[(unsigned int)*pa++];
    *pb = 0;
 
    printf("%s\n", b);
    return EXIT_SUCCESS;
}

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