getchar returns a different character

Question

I'm trying to make a program I already made more organized by using functions. the purpose of it is processing a menu with several options for calculating different values. This code is for processing the Main menu, and the error I'm getting is that every character I type comes out as invalid (activates the default case in the switch) even if it is 1, 2 or 3, which are the possible options. What am I doing wrong?

void process_main_menu(){ int c; print_main_menu(); int option=getchar(); while((c=getchar())!='\n' && c!=EOF); switch(option){ case 1: program_state=ST_MENU_BASS; break; case 2: program_state=ST_MENU_TREBLE; break; case 3: program_state=ST_EXIT_PROGRAM; break; default: fprintf(stderr, "%s\n", MSG_INVALID_NUMBER); program_state=ST_MAIN_MENU; } }

I'm updating the code as I see it wasn't complete enough. I'm actually using macros for this

#include <stdio.h> #include <math.h> #include <string.h> #include <stdlib.h> #define OPT_MENU_BASS 1 #define OPT_MENU_TREBLE 2 #define OPT_EXIT_PROGRAM 3 typedef enum { ST_MAIN_MENU, ST_MENU_BASS, ST_MENU_TREBLE, ST_EXIT_PROGRAM, ST_MENU_TREBLE_FREQ, ST_MENU_TREBLE_GAIN, ST_MENU_TREBLE_FREQ_FREQ_TREBLE, ST_MENU_TREBLE_FREQ_RESISTOR_3, ST_MENU_TREBLE_FREQ_CAPACITOR_3, ST_MENU_TREBLE_GAIN_RES5, ST_MENU_BASS_FREQ, ST_MENU_BASS_GAIN, ST_MENU_BASS_FREQ_FREQ_BASS, ST_MENU_BASS_FREQ_RESISTOR_2, ST_MENU_BASS_FREQ_CAPACITOR_1, ST_MENU_BASS_GAIN_RESISTOR_1, } state_t; state_t program_state; void process_main_menu(){ int c; print_main_menu(); char option=getchar(); while((c=getchar())!='\n' && c!=EOF); switch(option){ case OPT_MENU_BASS: program_state=ST_MENU_BASS; break; case OPT_MENU_TREBLE: program_state=ST_MENU_TREBLE; break; case OPT_EXIT_PROGRAM: program_state=ST_EXIT_PROGRAM; break; default: fprintf(stderr, "%s\n", MSG_INVALID_NUMBER); program_state=ST_MAIN_MENU; } }

The most basic debugging technique when something goes wrong like this is 'print the value the program actually read'. Include fprintf(stderr, "Got %d ('%c')\n", option, option); in the default clause and you'd see the information that you typed 49 ('1') which would strongly hint at why you have a problem. It takes, perhaps, a bit more experience to know to print both the numeric and character versions of the value in option, but it becomes automatic over time. — Jonathan Leffler
– Jonathan Leffler, Commented Oct 24, 2016 at 3:46
Thank you for your completed post. You still cannot use case OPT_MENU_BASS: unless you do case (OPT_MENU_BASS + '0'): because OPT_MENU_BASS is equal to decimal 1 not character '1' (which is actually decimal 49) or you can do switch(option - '0') to make option a decimal instead of a character. Look carefully at e.g. ASCII Table.com. Alternatively you could #define OPT_MENU_BASS '1', but the redefinition of OPT_MENU_BASS would likely cause issues elsewhere in your code. — David C. Rankin
– David C. Rankin, Commented Oct 24, 2016 at 4:01
Thank you for your answer, but all of those options still give me the same error. I'll figure it out somehow — Andibadia
– Andibadia, Commented Oct 24, 2016 at 4:24

dbush · Accepted Answer · 2016-10-24 12:31:14Z

4

You're reading in a character such as , which is stored as its ASCII code, not a numerical value.

You need to change your cases to look for the character '1', not the number 1.

 case '1': program_state=ST_MENU_BASS; break; case '2': program_state=ST_MENU_TREBLE; break; case '3': program_state=ST_EXIT_PROGRAM; break;

EDIT:

Given the macros you're using, you need to modify the macros to represent the characters '1', '2' or '3' instead of the numbers 1, 2 or 3.

#define OPT_MENU_BASS '1' #define OPT_MENU_TREBLE '2' #define OPT_EXIT_PROGRAM '3'

edited Oct 24, 2016 at 12:31

answered Oct 24, 2016 at 3:06

dbush

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5 Comments

Andibadia Over a year ago

Thanks for answering! Your solution works, but only for 2 and 3; if i type 1 it returns 2 messages of invalid numbers. Also, originally (and how it was supposed to be) replacing the numbers i had macros, like OPT_MENU_BASS assigned to values 1, 2 and 3, how could i do it using that?

David C. Rankin Over a year ago

Without seeing more of your code, all we can do is guess that you properly declare the global program_state and have properly defined the macros ST_MENU_BASS, ST_MENU_TREBLE, ST_EXIT_PROGRAM. We're good, but we cannot see your display from here...

dbush Over a year ago

@Andibadia See my edit. You need to change the macros to use character constants, not numerical constants.

Andibadia Over a year ago

Yes, that worked! At first it didn't but I had a stupid error in my code that made me think that it didn't work. Thank you very much

dbush Over a year ago

@Andibadia Glad I could help. Feel free to accept this answer if you found it useful.

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