Scanf in visual studio not accepting multiple cases of characters - c

Question

I'm creating a conversion project for letters/numbers ASCII table. My code is supposed to be 'interactive', so the user would type 'y' or 'n' to answer questions on the screen. However, it doesn't want to do this twice...
I have tried:
Just trying numbers instead of characters, but it's not exactly what I want
The %[\n]*c, and %[\n]c, and %[\n]*s ... technique but it doesn't help ;-;
Testing in a different project, but the only way I am able to do it is for multiple scanf()s to be in a row.
Here is the code:
printf("Would you like to convert a number today? \n");
printf("Please press Y or N \n");
scanf("%c", &input);
if (input == 'y' || input == 'Y') { //compare input if they said 'yes'
printf("\nThank you! \nWhat number?\n");
scanf("%d", &number);
flag = test(number);
if (flag == 0) { //if there is an equivalent letter
letter = conversion(number); //find the equivalent letter
printf("\nYour Number \t ASCII letter\n");
printf("%d\t %c\n", number, letter);
}
}
else if (input == 'n' || input == 'N') {
printf("\nWould you like to convert a letter instead? This time enter 0 or 1\!\n\n"); //problem here!!
printf("I wish I could say it was to \' Spice things up \' ...but it\'s not ;-; \n\n");
scanf("%d", &input2);
if (input2 == 0) { //this needs to be checking whether the user input Y/y
printf("Great choice adventurer!\n");
printf("What letter will it be today?\n\n");
//..I would go to a different funtion here ie: test2(letter)...
scanf("%d", &number); //I showed that it worked with multiple numbers, but I can't get this to work with multiple letters
printf("%d", number);
}
if (input2 == 1) { //this needs to be checking whether the user input N/n
printf("Difficult to please, I see...\n\n");
printf("I suggest you move on with that attitude!\n\n");
printf("Bye bye then\n");
}
}
else { //if they tried to break the code
printf("Sorry I did not recognise your command...please retry\n");
printf("Press Y or N next time!\n");
}
The first check works perfectly, I just want the second check to be like the first!
Some 'solutions' caused a overflow, which I don't want if possible
Even if someone could explain why this isn't working the way I intended would be very helpful!

Answer 1

I'm not sure what confuses you.
Use
char foo;
scanf(" %c", &foo);
for single characters, eg. letters and
int bar;
scanf("%d", &bar);
for numbers, integers. If you type a letter instead, scanf() will fail.
%[...] is for strings.
scanf() returns the number of successful conversions (or EOF), so for
int height;
int width;
scanf("%d %d", &height, &width);
it returns 2 if successful. It might return 1 if only height could be read.
So to check for errors on user input you should do:
int height;
int width;
if (scanf("%d %d", &height, &width) != 2) {
// handle the error, maybe exit the program.
}
Your code could look like that (without error handling):
#define _CRT_SECURE_NO_WARNINGS // you said Visual Studio? Without it you should get
// warnings about some functions being insecure.
#include <ctype.h> // isalpha() returns true if the value is a letter
#include <stdlib.h> // EXIT_SUCCESS
#include <stdio.h> // puts(), printf(), scanf()
int main(void)
{
for(;;) { // for-ever ... endless loop since the user exits by answering
// 'n' or 'N' two times
puts("Would you like to convert a number today?\nPlease press Y or N:");
char input;
if (scanf(" %c", &input) != 1) // We reached EOF ... end of file
break; // that's improbable for stdin,
// but input could be redirected to
// read from a file instead.
if (input == 'y' || input == 'Y') {
puts("\nThank you!\nWhat number?");
int number;
scanf("%d", &number);
if (isalpha((char unsigned)number)) // *)
printf("\nYour Number \t ASCII letter\n%d\t %c\n\n", number, number);
else
puts("Sorry, but that's not the ASCII code of a letter :(\n");
}
else if (input == 'n' || input == 'N') {
puts("\nWould you like to convert a letter instead?\nPlease press Y or N:");
scanf(" %c", &input);
if (input == 'y' || input == 'Y') {
puts("\nGreat choice adventurer!\nWhat letter will it be today?");
char letter;
scanf(" %c", &letter);
if (isalpha(letter))
printf("\nYour letter \t ASCII code\n%d\t %c\n\n", letter, letter);
else
puts("Sorry, but that's not a letter :(\n");
}
else if (input == 'n' || input == 'N') {
puts("\nDifficult to please, I see...\n\nI suggest you move on with that attitude!\n");
puts("Bye bye then.");
return EXIT_SUCCESS;
}
}
else {
puts("Sorry I did not recognize your command... Please retry.");
puts("Press Y or N next time!\n");
}
}
}
*) isalpha() (and the other functions in <ctype.h>) expects a value that fits in a unsigned char or the value EOF. It has undefined behaviour for other values. Since we read user input into an int we cannot be sure that's the case so we have to cast the value to unsigned char before passing it to isalpha() (and friends).
Next time you ask a question please include your full code, including variable declarations, functions like test() and conversion() and #includes. But please, post an example that focuses on your problem at hand. All that dialog you included would not have been necessary.