Thread: 'a' undeclared (first use in this function) Error

Hello Programmers, I am trying to make a program that will allow a user to enter their name, from this point, three options should be present for the user to choose, then from that point, two more options should be present. I have if else statements in a switch case and I get the "undeclared" error for the a in the first " if(specificage == a) ". Does anyone know the fix to this, it is the only error I get. I'm new to programming, sorry if I sound like a rookie. Run it if you need, thanks!

NOTE: I use Code::Blocks.

Here is the code:

Code:

#include <stdio.h>
#include <string.h>


int main()
{
    char name[50];
    char ageclass[50];
    char specificage[50];


    printf("Please enter your name: ");
    fgets(name, 50, stdin);
    printf("Hello %s", name);


    printf("Are you a:\n");
    printf("1. Minor\n");
    printf("2. Adult\n");
    printf("3. Senior Citizen\n");
    printf("Answer(1, 2, or 3): ");
    fgets(ageclass, 50, stdin);


    switch (ageclass[50])
    {
        case'1':
        {
            printf("You are between the ages of:\n");
            printf("a. 0-12\n");
            printf("b. 13-18\n");
            printf("Answer(a or b): ");
            fgets(specificage, 50, stdin);
               if(specificage == a)
                {
                    printf("You are a young minor.");
                }
                else
                {
                    printf("You are an older minor.");
                }
        }


        case'2':
        {
            printf("You are between the ages of:\n");
            printf("a. 19-50\n");
            printf("b. 51-65\n");
            printf("Answer(a or b): ");
            fgets(specificage, 50, stdin);
                if(specificage == a)
                {
                    printf("You are a young adult.");
                }
                else
                {
                    printf("You are an older adult.");
                }
        }


        case'3':
        {
            printf("You are between the ages of:\n");
            printf("a. 66-90\n");
            printf("b. 91-110\n");
            printf("Answer(a or b): ");
            fgets(specificage, 50, stdin);
                if(specificage == a)
                {
                    printf("You are a young senior citizen.");
                }
                else
                {
                    printf("You are an older senior citizen.");
                }
        }
    }


    getchar();
    return 0;
}

Originally Posted by anduril462

You have two problems. First

Code:

if(specificage == a)

a here is treated as a variable. If you want to check that the user input the letter a, you need to put single quotes around it: 'a'. If you want a string containing one character, the letter a, use double quotes: "a"

Second, specificage is a char array/string. You can't compare strings with ==. You can compare individual characters in the string/array with ==, or use strcmp/strncmp:

Code:

if (strcmp(specificage, "some string") == 0)  // strcmp returns 0 if they're equal
// or
if (specificage[3] == 'q')  // check that the 4th (remember, arrays in C start at 0) character is a 'q'

I'm guessing you were more interested in the second example.

Two more notes:
1. fgets leaves the newline character (remember, the user pressed enter after 'a' or 'b'). If I enter "foo" followed by enter, the string fgets gives back contains "foo\n". If you do strcmp, it will not match "foo", since the \n is significant. If you need to get rid of it, use the strchr trick here: FAQ > Get a line of text from the user/keyboard (C) - Cprogramming.com.
2. The user may enter uppercase 'A' or 'B' for some reason, your program should handle it. Easy enough, use the toupper() or tolower() functions before comparing (remember to #include <ctype.h>)

Oh, actually this helped a lot, I will make these changes, thank you tons!
Could you check out my other post, the more recent one, thanks! It involves the same program.