#include <stdio.h>
#include <string.h>

#define ESCAPE_SEQS \
    X('\a', 'a') X('\b', 'b') X('\f', 'f') X('\n', 'n') \
    X('\r', 'r') X('\t', 't') X('\v', 'v') 

#define SIZE 1000

void escape(char *s, char *t);
void unescape(char *s, char *t);

/* runs escape and unescape on stdin, prints results*/
int main()
{
    int i, c;
    char s[SIZE+1], t[2*SIZE+1];

    for (i = 0; (c = getchar()) != EOF; i++) {
        if (i >= SIZE) {
            printf("warning : buffer overflow\n");
            break;
        }
        s[i] = c;
    }
    s[i] = '\0';
    escape(s, t);
    printf("--- escaped ---\n%s\n", t);

    unescape(t, s);
    printf("\n-- unescaped --\n%s", s);
    return 0;
}

/* escape: makes escape sequences visible as it copies s to t
 * size of t must be 2*size of s */ 
void escape(char *s, char *t)
{
    for (; *s != '\0'; s++, t++)
        switch (*s) {
            #define X(e, c) case e : *(t++) = '\\'; *t = c; break;
                ESCAPE_SEQS
            #undef X
            default : *t = *s; break;
        }
    *t = '\0';
}

/* unescape: inverse of escape */
void unescape(char *s, char *t)
{
    for (; *s != '\0'; s++, t++) {
        if (*s == '\\')
            switch (*(s+1)) {
                #define X(e, c) case c : *t = e; s++; continue;
                    ESCAPE_SEQS
                #undef X
            }
        *t = *s; 
    }
    *t = '\0';
}