C - 函数类型冲突错误

我是 C 新手。我试图从用户那里获取大量文本并计算单词、字符、行、空格和字母的数量。这就是我所做的：

#include <ctype.h>
#include <stdio.h>
int main(void)
{
    char c = getchar();
    char previousc;
    int charcount = 0;
    int wordcount = 0;
    int whitespacecount = 0;
    int linecount = 0;
    int lettercount = 0;
    while(c != EOF)
    {
            if(isLetter(c) == 1) lettercount++;
            if(isWhitespace(c) == 1)
            {
                    whitespacecount++;
                    if(isWhitespace(previousc) == 0) wordcount++;
            }
            if(c == "\n") linecount++;
            previousc = c;
            c = getchar();
            charcount++;
    }
    printf("Character Count: %d\n Word Count: %d\n Whitespace Count: %d\n Letter Count: %d\n Line Count: %d\n", charcount, wordcount, whitespacecount, linecount, lettercount);
}
int isLetter(char c) // 1 for true, 0 for false.
{
    // instead of writing tons of if's
    if(isalpha(c) > 0)
            return 1;
    return 0;
}
int isWhitespace(char c) // 1 for true, 0 for false.
{
    if(c == "\n" || c == " " || c == "      ") return 1;
    return 0;
}

但我收到了很多错误和警告，我迷失了......

program2.c: In function ‘main’:
program2.c:20: warning: comparison between pointer and integer
program2.c: At top level:
program2.c:28: error: conflicting types for ‘isLetter’
program2.c:28: note: an argument type that has a default promotion can’t match an empty parameter name list declaration
program2.c:14: error: previous implicit declaration of ‘isLetter’ was here
program2.c:35: error: conflicting types for ‘isWhitespace’
program2.c:35: note: an argument type that has a default promotion can’t match an empty parameter name list declaration
program2.c:15: error: previous implicit declaration of ‘isWhitespace’ was here
program2.c: In function ‘isWhitespace’:
program2.c:36: warning: comparison between pointer and integer
program2.c:36: warning: comparison between pointer and integer
program2.c:36: warning: comparison between pointer and integer

我用谷歌搜索了不同的错误，但没有找到解决我的问题的解决方案。

你能帮我一下吗？

Thanks.

For

program2.c:20：警告：指针和整数之间的比较

Change

 if(c == "\n")  

to

 if(c == '\n')  

For

program2.c:28：错误：“isLetter”的类型冲突
program2.c:28：注意：具有默认提升的参数类型不能与空参数名称列表声明匹配
program2.c:14: 错误：之前的隐式声明‘isLetter’在这里
program2.c:35：错误：“isWhitespace”的类型冲突
program2.c:35：注意：具有默认提升的参数类型不能与空参数名称列表声明匹配 program2.c:15: 错误：之前的隐式声明‘isWhitespace’在这里

为您的函数定义原型。

int isLetter(char c);
int isWhitespace(char c);  

For

program2.c：在函数“isWhitespace”中：
program2.c:36：警告：指针和整数之间的比较
program2.c:36：警告：指针和整数之间的比较
program2.c:36：警告：指针和整数之间的比较

Change

if(c == "\n" || c == " " || c == "      ") return 1;

to

if(c == '\n' || c == ' ' || c == '\t')