我的代码如下：
#include <stdio.h>
#include <stdlib.h>
int isUpper(char*);
int causeUpper(char*);
int causeLower(char*);
int isNumber(char*);
int main(void)
{
char userInput[1];
int caseResult;
int numResult;
char newUpper;
char newLower;
printf("Input a character: ");
scanf("%c", userInput);
numResult = isNumber(userInput);
if (numResult == 0)
{
caseResult = isUpper(userInput);
if (caseResult == 0);
{
newUpper = causeUpper(userInput);
printf("%c\n", newUpper);
}//close of if statement
if (caseResult == 1)
{
newLower = causeLower(userInput);
printf("%c\n", newLower);
}//close of if statement
}//close of if statement
if (numResult == 1)
{
printf("%d\n", userInput);
}//close of if statement
if (userInput == ",")
{
exit;
}//close of if statement
}//close of main function
int isUpper(char* userInput)
{
if (*userInput > 64 && *userInput < 91)
{
return 1;
}//close of if statement
else
{
return 0;
}//close of else statement
}//close of isUpper function
int causeUpper(char* userInput)
{
*userInput = *userInput - 32;
return *userInput;
}//close of causeUpper function
int causeLower(char* userInput)
{
*userInput = *userInput + 32;
return *userInput;
}//close of causeLower function
int isNumber(char* userInput)
{
int numResult;
if (*userInput >= '0' && *userInput <= '9')
{
numResult = 1;
return numResult;
}//close of if statement
else
{
numResult = 0;
return numResult;
}//close of else statement
}//close of isNumber function
我对我的代码进行了建议编辑，当我运行它时输入了＆＃39; a＆＃39;变成'A＆＃39;，这样可行，但是当我尝试测试下一个功能时，输入A＆＃39; A＆＃39;返回此而不是小写字母：
!
A
如何修复此错误，以便在输入大写字母时只输出小写字母？