切换字符大小写，指针问题

Question

The goal of my program is to switch the cases of the two letters inputted. For example a turns to A and B turns to b. I am having trouble getting my code to work when I know my logic is correct.

#include <stdio.h>;

void switcharoo(char *ch1,char *ch2)
{

    if(*ch1 >= 'a' && *ch1 <= 'z' && *ch2 >= 'A' && *ch2 <= 'Z')
    {
        *ch1 = 'A' + *ch1 - 'a';
        *ch2 = 'a' + *ch2 - 'A';
    }
    else if(*ch1 >= 'A' && *ch1 <= 'Z' && *ch2 >= 'A' && *ch2 <= 'Z')
    {
        *ch1 = 'a' + *ch1 - 'A';
        *ch2 = 'a' + *ch2 - 'A';
    }
    else if(*ch1 >= 'a' && *ch1 <= 'z' && *ch2 >= 'a' && *ch2 <= 'z')
    {
        *ch1 = 'A' + *ch1 - 'a';
        *ch2 = 'A' + *ch2 - 'a';
    }
    else if(*ch1 >= 'A' && *ch1 <= 'Z' && *ch2 >= 'a' && *ch2 <= 'z')
    {
        *ch1 = 'a' + *ch1 - 'A';
        *ch2 = 'A' + *ch2 - 'a';
    }
}

int main()
{
    char lettera,letterb;

    printf("Please input a first character: ");
    scanf("%c", &lettera);
    printf("Please input a first character: ");
    scanf("%c", &letterb);

    switcharoo(lettera,letterb);
    printf("%c\n %c\n",lettera,letterb);

    return 0;
}

Answer 1

scanf("%c", &lettera);
scanf("%c", &letterb);

This probably isn't doing what you want. The newline (enter) character you presumably type after entering the first letter (given your prompts imply you're expecting them on different lines) will be read in as the second letter. You'd have to type two letters then a newline for them to be read into your lettera and letterb successfully... can just prompt once for 2 characters. Also, it's good practice to check the return value of scanf to ensure it got the input you requested....

Answer 2

Unless I am required to create my own function, I'd use #include <ctype.h> functions to make my life easier.

#include <ctype.h>
#include <stdio.h>

int main()
{
    char lettera,letterb;

    printf("Please input a first character: ");
    scanf("%c", &lettera);
    printf("Please input a first character: ");
    scanf(" %c", &letterb); // note the space in front of %c to flush '\n'

    // lettera conversion
    if(isupper(lettera)) {
        lettera = tolower(lettera);
    } else if (islower(lettera)) {
        lettera = toupper(lettera);
    }

    // letterb conversion
    if(isupper(letterb)) {
        letterb = tolower(letterb);
    } else if (islower(letterb)) {
        letterb = toupper(letterb);
    }

    printf("%c\n %c\n",lettera,letterb);

    return 0;
}

Answer 3

You should call

switcharoo(lettera,letterb);

as

switcharoo(&lettera,&letterb); //passing address of lettera and letterb

as you are taking char * in the function.

Answer 4

Your code will not run. The compiler will give error as con not convert char to char *.

Try calling your function the way Rohan has suggested.

Or you can simplify your function. Use it for one parameter only and call it twice.

char changeCase(char ch) {
  if (ch >= 'A' && ch <= 'Z')
    ch -= 32;
  if (ch >= 'a' && ch <= 'z')
    ch += 32;
  return ch;
}

In main you can write,

char lettera, letterb;
//get values of lettera and letterb
lettera = changeCase(lettera);
letterb = changeCase(letterb);