#include<stdio.h>
void main()
{
    char ch;
    scanf("%c",&ch);
    if(ch>='A'&&ch<='Z')
    {
        ch=+32;
    printf("%ch\n",ch);
    }
    else
        if(ch>='a'&&ch<='z')
        {
            ch=-32;
        printf("%ch\n",ch);
        }
            else
            if(ch>=48&&ch<=57)
            {
                printf("%x\n",ch);
            }
                else
                printf("control key\n");
}

printf("%ch\n",ch);首先这里错了.应该是printf("%c\n",ch);％后面应该是%d,%lf,%f,%c分别是整型，双．单整型和字符常量．
ch=+32;你的意思应该是ch+=32:是ch=ch+32;吧．
我也是初学者，可能有错的，可以讨论的．
我的ＱＱ４８９６６７１２５

#include<stdio.h>
void main()
{
    char ch;
    scanf("%c",&ch);
    if(ch>='A'&&ch<='Z')
    {
        ch+=32;
    printf("%c\n",ch);
    }
    else
        if(ch>='a'&&ch<='z')
        {
            ch-=32;
        printf("%c\n",ch);
        }
            else
            if(ch>=48&&ch<=57)
            {
                printf("%x\n",ch);
            }
                else
                printf("control key\n");
}

#include<stdio.h>
void main()
{
    char ch;
    scanf("%c",&ch);
    if(ch>='A'&&ch<='Z')
    {
        ch+=32;
    printf("%c\n",ch);
    }
    else
        if(ch>='a'&&ch<='z')
        {
            ch-=32;
        printf("%c\n",ch);
        }
            else
            if(ch>=48&&ch<=57)
            {
                printf("%x\n",ch);
            }
                else
                printf("control key\n");
}

不小心，点了两次，不好意思。

谢谢，帮助