c代码：电话号码和字母转换

这两天看到有人讨论电话键盘上的字母、号码和字母的转换，我也随便写了一段

#include <stdio.h>#include <string.h>#include <ctype.h>#define MAX_LEN 15char *tbl_itoa[] ={"0", // 0"1", // 1"ABC", // 2"DEF", // 3"GHI", // 4"JKL", // 5"MNO", // 6"PQRS", // 7"TUV", // 8"WXYZ" // 9};int tbl_atoi['Z'-'A'+1] = {0};void init_tbl(){int c;int i;for (c='A'; c<='Z'; c++){for (i=0; i<=9; i++){if (strchr(tbl_itoa[i], c) != NULL){tbl_atoi[c-'A'] = i;break;}}}#if 0 // DEBUGfor (c='A'; c<='Z'; c++){printf("%c %d/n", (char)c, tbl_atoi[c-'A']);}#endif}void to_digits(const char *s);void to_alpha(const char *s);int is_all_digits(const char *s);int main(int argc, char *argv[]){if (argc < 2){printf("Usage: %s STRING/n", argv[0]);return 1;}if (strlen(argv[1]) > MAX_LEN){printf("string too long. only %d allowed/n", MAX_LEN);return 1;}init_tbl();if (is_all_digits(argv[1]))to_alpha(argv[1]);elseto_digits(argv[1]);return 0;}int is_all_digits(const char *s){char c;while ((c=*s++) != '/0')if (!isdigit(c))return 0;return 1;}void to_digits(const char *s){char c;while ((c=*s++) != '/0'){if (islower(c))c = toupper(c);if (isupper(c))printf("%d", tbl_atoi[(int)(c-'A')]);elseprintf("%c", c);}printf("/n");}void to_alpha(const char *s){char *p;static char result[MAX_LEN+2] = {0};static int idx = 0;if (!isdigit(*s)){result[idx] = '/0';printf("%s/n", result);idx--;return;}p = tbl_itoa[(int)(*s-'0')];while(*p){result[idx++] = *p;to_alpha(s+1);p++;}idx--;}