为什么我在字符串的末尾总是得到多余的字符？

Question

I have the string, "helLo, wORld!" and I want my program to change it to "Hello, World!". My program works, the characters are changed correctly, but I keep getting extra characters after the exclamation mark. What could I be doing wrong?

void normalize_case(char str[], char result[])
{
   if (islower(str[0]) == 1)
   {
      result[0] = toupper(str[0]);
   }

   for (int i = 1; str[i] != '\0'; i++)
   {
      if (isupper(str[i]) == 1)
      {
         result[i] = tolower(str[i]);
      }

      else if (islower(str[i]) == 1)
      {
         result[i] = str[i];
      }

      if (islower(str[i]) == 0 && isupper(str[i]) == 0)
      {
         result[i] = str[i];
      }

      if (str[i] == ' ')
      {
         result[i] = str[i];
      }

      if (str[i - 1] == ' ' && islower(str[i]) == 1)
      {
         result[i] = toupper(str[i]);
      }
   }
}  

Answer 1

Extra random-ish characters at the end of a string usually means you've forgotten to null-terminate ( '\\0' ) your string. Your loop copies everything up to, but not including, the terminal null into the result.

Add result[i] = '\\0'; after the loop before you return.

Normally, you treat the isxxxx() functions (macros) as returning a boolean condition, and you'd ensure that you only have one of the chain of conditions executed. You'd do that with more careful use of else clauses. Your code actually copies str[i] multiple times if it is a blank. In fact, I think you can compress your loop to:

int i;

for (i = 1; str[i] != '\0'; i++)
{
   if (isupper(str[i]))
       result[i] = tolower(str[i]);
   else if (str[i - 1] == ' ' && islower(str[i]))
       result[i] = toupper(str[i]);
   else
       result[i] = str[i];
}
result[i] = '\0';

If I put result[i] outside of the for loop, won't the compiler complain about i ?

Yes, it will. In this context, you need i defined outside the loop control, because you need the value after the loop. See the amended code above.

You might also note that your pre-loop code quietly skips the first character of the string if it is not lower-case, leaving garbage as the first character of the result. You should really write:

result[0] = toupper(str[0]);

so that result[0] is always set.

Answer 2

You are not null terminating result so when you print it out it will keep going until a null is found. If you move the declaration of i to before the for loop:

int i ;
for ( i = 1; str[i] != '\0'; i++)

you can add:

result[i] = '\0' ;

after the for loop, this is assuming result is large enough.

Answer 3

I took the liberty of simplifying your code as a lot of the checks you do are unnecessary. The others have already explained some basic points to keep in mind:

#include <stdio.h> /* for printf */
#include <ctype.h> /* for islower and the like */

void normalise_case(char str[], char result[])
{
    if (islower(str[0]))
    {
        result[0] = toupper(str[0]); /* capitalise at the start */
    }

    int i; /* older C standards (pre C99) won't like it if you don't pre-declare 'i' so I've put it here */

    for (i = 1; str[i] != '\0'; i++)
    {
        result[i] = str[i]; /* I've noticed that you copy the string in each if case, so I've put it here at the top */

        if (isupper(result[i]))
        {
            result[i] = tolower(result[i]);
        }

        if (result[i - 1] == ' ' && islower(result[i])) /* at the start of a word, capitalise! */
        {
            result[i] = toupper(result[i]);
        }

    }

    result[i] = '\0'; /* this has already been explained */
}

int main()
{
    char  in[20] = "tESt tHIs StrinG";

    char out[20] = ""; /* space to store the output */

    normalise_case(in, out);

    printf("%s\n", out); /* Prints 'Test This String' */

    return 0;
}

Answer 4

您应该在循环末尾添加语句result[i] = '\\0' ，因为在C语言中，字符串数组应以特殊字符'\\ 0'结尾，这告诉编译器“这是结束符”。字符串”。