#include <stdio.h>
#include <stdlib.h>
int ccc(char ch);

//子函数，判断输入是否为字符，并返回字符的数值位置
int ccc(char ch)
{
    int i,num;
    i = ch;
    if(i>=65 && i<=90)
    {
        num = i-65+1;
        return num;
    }
    else if(i>=97 && i<=122)
    {
        num = i-97+1;
        return num;
    }
    else
        return -1;

}

int main(void)
{
    int a,i;
    char c;
    printf("input the char.\n");
    scanf("%c",&c);
    a=ccc(c);
    if(a != -1)
    {
        printf("%c is a char and is %d.",c,a);
    }
    else
        printf("%c is not a char.\n");


    return 0;
}

#include <stdio.h>
#include <stdlib.h>
int ccc(char *ch);

//子函数，判断输入是否为字符，并返回字符的数值位置
int ccc(char *ch)
{
    int i,num;
    i = ch;
    if(i>=65 && i<=90)
    {
        num = i-65+1;
        return num;
    }
    else if(i>=97 && i<=122)
    {
        num = i-97+1;
        return num;
    }
    else
        return -1;

}

int main(void)
{
    int a,i;
    char c[20],*p;
    printf("input the char.\n");
    p = c;
    scanf("%20s",&c);
    while(*p != '\0')
    {
        a=ccc(p);
    if(a != -1)
    {
        printf("%c is a char and is %d.",c,a);
    }
    else
        printf("%c is not a char.\n");

        p++;

    }

    return 0;
}
修改了一下，输出全部变成了
 is not a char.
 is not a char.
 is not a char.

i = ch;
改成
i = *ch;
成功了