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Question

今天，我解决了Google的一个问题:模仿手机键盘短信。

下面是带有goto语句的程序。我知道使用goto是一种非结构化的风格，但我仍然这样做，因为它提高了速度。

#include <stdio.h>

int main()
{
    char c, c1 = NULL;
    int top;

    top:
    while((c = getchar()) != '\n')
    {
        if (c == ' ')printf("0");

        if(c == 'a' || c == 'b' || c == 'c')
        {
           if(c1 == 'a' || c1 == 'b' || c1 == 'c')
           printf(" ");
          if(c == 'a') printf("2");
          if(c == 'b') printf("22");
          if(c == 'c') printf("222");
           c1 = c;
            goto top;

        }


         if(c == 'd' || c == 'e' || c == 'f')
        {
          if(c1 == 'd' || c1 == 'e' || c1 == 'f')
           printf(" ");
          if(c == 'd') printf("3");
          if(c == 'e') printf("33");
          if(c == 'f') printf("333");
           c1 = c;
            goto top;


        }

         if(c == 'g' || c == 'h' || c == 'i')
        {
            if(c1 == 'g' || c1 == 'h' || c1 == 'i')
           printf(" ");

          if(c == 'g') printf("4");
          if(c == 'h') printf("44");
          if(c == 'i') printf("444");
           c1 = c;
            goto top;

        }



         if(c == 'j' || c == 'k' || c == 'l')
        {
            if(c1 == 'j' || c1 == 'k' || c1 == 'l')
           printf(" ");

          if(c == 'j') printf("5");
          if(c == 'k') printf("55");
          if(c == 'l') printf("555");
           c1 = c;
            goto top;


        }

         if(c == 'm' || c == 'n' || c == 'o')
        {
            if(c1 == 'm' || c1 == 'n' || c1 == 'o')
           printf(" ");

          if(c == 'm') printf("6");
          if(c == 'n') printf("66");
          if(c == 'o') printf("666");
           c1 = c;
            goto top;


        }

          if(c == 'p' || c == 'q' || c == 'r' || c == 's')
        {
            if(c1 == 'p' || c1 == 'q' || c1 == 'r' || c1 == 's')
           printf(" ");

          if(c == 'p') printf("7");
          if(c == 'q') printf("77");
          if(c == 'r') printf("777");
          if(c == 's') printf("7777");
           c1 = c;
            goto top;

        }

          if(c == 't' || c == 'u' || c == 'v')
        {
            if(c1 == 't' || c1 == 'u' || c1 == 'v')
           printf(" ");

          if(c == 't') printf("8");
          if(c == 'u') printf("88");
          if(c == 'v') printf("888");
           c1 = c;
           goto top;

        }

          if(c == 'w' || c == 'x' || c == 'y' || c == 'z')
        {
            if(c1 == 'w' || c1 == 'x' || c1 == 'y' || c1 == 'z')
           printf(" ");
          if(c == 'w') printf("9");
          if(c == 'x') printf("99");
          if(c == 'y') printf("999");
          if(c == 'z') printf("9999");
           c1 = c;
          goto top;

        }
    }
}

上面没有goto的程序：

#include <stdio.h>

int main()
{
    char c, c1 = NULL;

    while((c = getchar()) != '\n')
    {
        if (c == ' ')printf("0");

        if(c == 'a' || c == 'b' || c == 'c')
        {
           if(c1 == 'a' || c1 == 'b' || c1 == 'c')
           printf(" ");
          if(c == 'a') printf("2");
          if(c == 'b') printf("22");
          if(c == 'c') printf("222");

        }


         if(c == 'd' || c == 'e' || c == 'f')
        {
          if(c1 == 'd' || c1 == 'e' || c1 == 'f')
           printf(" ");
          if(c == 'd') printf("3");
          if(c == 'e') printf("33");
          if(c == 'f') printf("333");


        }

         if(c == 'g' || c == 'h' || c == 'i')
        {
            if(c1 == 'g' || c1 == 'h' || c1 == 'i')
           printf(" ");

          if(c == 'g') printf("4");
          if(c == 'h') printf("44");
          if(c == 'i') printf("444");

        }



         if(c == 'j' || c == 'k' || c == 'l')
        {
            if(c1 == 'j' || c1 == 'k' || c1 == 'l')
           printf(" ");

          if(c == 'j') printf("5");
          if(c == 'k') printf("55");
          if(c == 'l') printf("555");


        }

         if(c == 'm' || c == 'n' || c == 'o')
        {
            if(c1 == 'm' || c1 == 'n' || c1 == 'o')
           printf(" ");

          if(c == 'm') printf("6");
          if(c == 'n') printf("66");
          if(c == 'o') printf("666");


        }

          if(c == 'p' || c == 'q' || c == 'r' || c == 's')
        {
            if(c1 == 'p' || c1 == 'q' || c1 == 'r' || c1 == 's')
           printf(" ");

          if(c == 'p') printf("7");
          if(c == 'q') printf("77");
          if(c == 'r') printf("777");
          if(c == 's') printf("7777");

        }

          if(c == 't' || c == 'u' || c == 'v')
        {
            if(c1 == 't' || c1 == 'u' || c1 == 'v')
           printf(" ");

          if(c == 't') printf("8");
          if(c == 'u') printf("88");
          if(c == 'v') printf("888");


        }

          if(c == 'w' || c == 'x' || c == 'y' || c == 'z')
        {
            if(c1 == 'w' || c1 == 'x' || c1 == 'y' || c1 == 'z')
           printf(" ");
          if(c == 'w') printf("9");
          if(c == 'x') printf("99");
          if(c == 'y') printf("999");
          if(c == 'z') printf("9999");


        }

        c1 = c;
    }
}

哪一个更好？我如何才能认识到X程序比Y更好？

顺便说一句，我没有使用任何派生数据类型和指针，因为我发现它在这里没有用。

Answer 1

在过去的几年里，我没有编写任何C语言，但是我认为您可以在第一个版本中使用continue而不是goto。

Answer 2

因为你的外层测试是相互排斥的。)，您应该使用else而不是goto或continue。当else测试的条件为false时，将使用if：

    if (c == ' ') {
        printf("0");
    }
    else if (c == 'a' || c == 'b' || c == 'c')
    {
        if(c1 == 'a' || c1 == 'b' || c1 == 'c')
            printf(" ");
        if(c == 'a') printf("2");
        else if(c == 'b') printf("22");
        else if(c == 'c') printf("222");
        c1 = c;
    }
    else if(c == 'd' || c == 'e' || c == 'f')
    { ... }
    else if ...
etc

还要注意，c和c1应该声明为int，而c1 = NULL是错误的(因为NULL被声明为(void *) 0；使用c1 = '\0' )。

此外，在编译器中打开更多警告。