一个简短的程序，接受输入的小写字母，它给出大写字母，并在按Enter键时退出

Question

The conversion works correctly but when I press enter, when asked for a lower case, it executes an enter (\\n) and doesn't exit or stop.

This is my program:

#include <stdio.h>
#include <math.h>



main()
{
 char ch;
 printf("Press a letter: ");
 while (scanf(" %c",&ch)!='\n')
    {
        printf("%c\n",ch-32);     
    }


}

Answer 1

Your program is incorrect:

• scanf does not return the character that has been read, it returns the number of scanned items
• One way to deal with '\\n' is to check if (ch == '\\n') break;
• You need to check if a character is indeed a letter before subtracting 32
• You should use a toupper function instead of using subtraction directly.

Answer 2

use this code :

#include <stdio.h>
#include <math.h>        

    main()
    {
     char ch;
     printf("Press a letter: ");
     while (1)
        {
           scanf(" %c",&ch);
           if(ch=='\n')
               break;
           printf("%c\n",ch-32);     
        }
    }

Answer 3

scanf(" %c",&ch) will never set ch to \\n as the space in the format consumes all white-space, including '\\n' before moving on to "%c" .

Further, the return value from scanf() is EOF or the number of successfully parsed arguments, not ch . (not "%n" though)

Consider:

#include <stdio.h>
// No need for #include <math.h>
#include <ctype.h>

int main() {
  int ch;  // use int
  printf("Press a letter: ");
  while ((ch = fgetc(stdin)) != EOF && (ch != '\n')) {
    printf("%c\n", toupper(ch));     
  }
  return 0; 
}

OP states in another comment "we should perform this without using outside functions, for example, my professor didn't teach us toupper". Let's assume stdio functions are OK and ctype ones are not.

  // Assume ASCII encoding

  while ((ch = fgetc(stdin)) != EOF && (ch != '\n')) {
    if ((ch >= 'a') && (ch <= 'z')) {
      ch += 'A' - 'a';
    }
    printf("%c\n", ch);     
  }

  // Not assuming ASCII encoding, but letters a-z, A-Z

  while ((ch = fgetc(stdin)) != EOF && (ch != '\n')) {
    static const char *az = "abcdefghijklmnopqrstuvwxyz";
    static const char *AZ = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    int i;
    for (i=0; az[i]; i++) {
      if (ch == az[i]) {
        ch = AZ[i];
        break;
      }
    }
    printf("%c\n", ch);     
  }