C-用指针的touper和toloter

Question

我正在尝试弄清楚如何使用指针使用toupper和tolower。我以为我在正确的道路上。我设法使大写字母正确的指针正确，但由于某种原因，它对小写不起作用。任何建议都会有所帮助。

#include <stdio.h>
#include <ctype.h>
void safer_gets (char array[], int max_chars);
main()
{
    /* Declare variables */
    /* ----------------- */
    char  text[51];
    char *s1_ptr = text;
    int   i;
    /* Prompt user for line of text */
    /* ---------------------------- */
    printf ("nEnter a line of text (up to 50 characters):n");
    safer_gets(text ,50);

    /* Convert and output the text in uppercase characters. */
    /* ---------------------------------------------------- */
    printf ("nThe line of text in uppercase is:n");
    while (*s1_ptr != '') 
        {
            *s1_ptr = toupper(*s1_ptr);          
            putchar(toupper(*s1_ptr++));
        }
    /* Convert and output the text in lowercase characters. */
    /* ---------------------------------------------------- */
    printf ("nnThe line of text in lowercase is:n");
    while (*s1_ptr != '') 
        {
            *s1_ptr = tolower(*s1_ptr);          
            putchar(tolower(*s1_ptr++));
        }
    /* Add carriage return and pause output */
    /* ------------------------------------ */
    printf("n");
    getchar();
} /* end main */
/* Function safer_gets */
/* ------------------- */
void safer_gets (char array[], int max_chars)
{
    /* Declare variables. */
    /* ------------------ */
    int i;
    for (i = 0; i < max_chars; i++)
        {
            array[i] = getchar();
            /* If "this" character is the carriage return, exit loop */
            /* ----------------------------------------------------- */
            if (array[i] == 'n')
                break;
        } /* end for */
    if (i == max_chars )
        if (array[i] != 'n')
            while (getchar() != 'n');
    array[i] = '';
} /* end safer_gets */

Answer 1

那是因为它永远不会进入第二个循环，因为您修改了指针。在第二个循环重置您的指针到S1_ptr =文本之前，它将起作用。