将换行符和制表符等字符转换为可见的转义序列，如/n和/t

#include <stdio.h>

#define MAXLINE 1000

int getchars(char line[], int maxline);
void escape(char s[], char t[]);
void unescape(char s[], char t[]);

int main(void){
    char t[MAXLINE] = "this is /na /ttest/" test /v test /r ";
    char s1[MAXLINE];
    char s2[MAXLINE];

    escape(s1, t);
    printf("/nescape result:/n%s/n", s1);

    unescape(s2, s1);
    printf("unescape result:/n%s/n", s2);

    return 0;
}
void escape(char s[], char t[]){
    int i, j;

    for (i = 0, j = 0; t[i] != '/0'; ++i) {
        switch (t[i]) {
        case '/n':
            s[j++] =  '//';
            s[j++] =  'n';
            break;
        case '/t':
            s[j++] =  '//';
            s[j++] =  't';
            break;
        case '/v':
            s[j++] =  '//';
            s[j++] =  'v';
            break;
        case '/b':
            s[j++] =  '//';
            s[j++] =  'b';
            break;
        case '/r':
            s[j++] =  '//';
            s[j++] =  'r';
            break;
        case '/f':
            s[j++] =  '//';
            s[j++] =  'f';
            break;
        case '/a':
            s[j++] =  '//';
            s[j++] =  'a';
            break;
        case '//':
            s[j++] =  '//';
            s[j++] =  '//';
            break;
        case '/?':
            s[j++] =  '//';
            s[j++] =  '/?';
            break;
        case '/'':
            s[j++] =  '//';
            s[j++] =  '/'';
            break;
        case '/"':
            s[j++] =  '//';
            s[j++] =  '/"';
            break;
        default:
            s[j++] = t[i];
            break;
        }
    }
    s[j] = '/0';
}

void unescape(char s[], char t[])
{
    int i, j;

    for (i = 0, j = 0; t[i] != '/0'; ++i) {
        if (t[i] == '//') {
            switch (t[++i]) {
            case 'n':
                s[j++] =  '/n';
                break;
            case 't':
                s[j++] =  '/t';
                break;
            case 'v':
                s[j++] =  '/v';
                break;
            case 'b':
                s[j++] =  '/b';
                break;
            case 'r':
                s[j++] =  '/r';
                break;
            case 'f':
                s[j++] =  '/f';
                break;
            case 'a':
                s[j++] =  '/a';
                break;
            case '//':
                s[j++] =  '//';
                break;
            case '/?':
                s[j++] =  '/?';
                break;
            case '/'':
                s[j++] =  '/'';
                break;
            case '/"':
                s[j++] =  '/"';
                break;
            // actually, cases below should never happen if the input string is correct.
            case '/0':
            default:
                s[j++] = '//';
                --i;
                break;
            }
        } else {
            s[j++] =  t[i];
        }
    }
    s[j] = '/0';
}