CODEWITHSUNDEEP
c
user2781018
user2781018

Reputation:

How Does Char Variable Work in C

What I am trying to accomplish is prompting the user with the question of do they want to run the program again. They either type y or n. If y, it reruns the program. If no, it stops the program. Anything other than those two will prompt an error and ask the question again. I'm used to C# where strings are not complicated, but in C, I guess there technically isn't strings, so we have to use either char arrays or char pointers. I've tried both, none that work that way I want, but I'm probably the problem. This is what I have. 

char answer[1] = "a";

while (strcmp(answer, "y") != 0 || strcmp(answer, "n") != 0)
{
    printf ("\n\nWould you like to run the program again? Type y or n. Then, hit Enter.");
    scanf ("%c", answer);

    if (strcmp(answer, "y") == 0)
    {
        main();
    }
    else if (strcmp(answer, "n") == 0)
    {
        continue;
    }
    else 
    {
        printf ("\nERROR: Invalid input was provided. Your answer must be either y or n. Hit Enter to continue.");
        F = getchar();
        while ((getchar()) != F && EOF != '\n');
    }
}

I have other while loops similar to this that work as expected, but use a float. So I'm assuming the problem is me using char here. What happens right now is that it doesn't even prompt the user for the question. It just asks the question and shows the error right afterwards. I'm sure there are other things wrong with this code, but since I can't get the prompt to work, I cannot test the rest of it yet.

Upvotes: 0

Views: 261

Answers (4)

Tyler Cloutier
Tyler Cloutier

Reputation: 2050

Here is one way to do it. It is by no means the only way to do it, but I think it accomplishes what you want. You should not call the main function recursively.

#include <stdio.h>
#include <stdlib.h>

void run_program()
{
    printf("program was run.");
}

int main() {
    char answer[2] = "y\0";
    int dump;    

    do {

        if (answer[0] == 'y')
        {
            run_program(); /* Not main, don't call main recursively. */
        }

        printf ("\n\nWould you like to run the program again? Type y or n. Then, hit Enter.\n");
        scanf ("%1s", answer);

        /* Dump all other characters on the input buffer to
           prevent continuous reading old characters if a user
           types more than one, as suggested by ThorX89. */
        while((dump=getchar())!='\n' && dump!=EOF); 

        if (answer[0] != 'n' && answer[0] != 'y')
        {
            printf ("Please enter either y or n\n");
        }

    } while (answer[0] != 'n');

    return 0;
}

Using %s instead of %c, reads in the new line so that the new line character is not in the stdin buffer which would become answer then next time scanf was called.

The run_program function is just a function where you would put your program's logic. You can call it whatever you want. I did this to separate out the menu logic from the logic of the actual program.

Upvotes: 0

Petr Skocik
Petr Skocik

Reputation: 60097

  • "a" is a string literal == char id[2]={'a','\0'} //Strings are char arrays terminated by zero, in C
  • 'a' is a char literal
  • strcmp is just "compare each char in two strings, until you hit '\0'"
  • scanf ("%c", ___); expect an address to write to as the second argument. Functions in C cannot modify their arguments (they don't have access to them--they get their own local copy) unless they have a memory address. You need to put &answer in there.

Jens has already basically answered the question, you most likely want to use getchar so that you can detect EOF easily. Unlike scanf("%c",...), getchar will not skip spaces, and I believe both versions will leave you with the unprocessed rest of the input line (a newline character ('\n') at least) after each getchar. You might want to something like 

int dump;
while((dump=getchar())!='\n' && dump!=EOF) {};

So that you discard the rest of the line once you've read your first character of it. Otherwise, the next getchar will get the next unprocessed character of the same line. ('\n' if the line was a single letter).

Upvotes: 1

Alessandro_ben
Alessandro_ben

Reputation: 1

Well, you are comparing two strings instead of characters. If you want to compare two character you have to follow this syntax:

char c;
scanf("%c",&c);

if(c == 'y')
    //do something
else
    //do nothing

Upvotes: -1

Jens
Jens

Reputation: 72697

I suggest using a light weight getchar() instead of the heavy scanf.

#include <stdio.h>

int c;  /* Note getchar returns int because it must handle EOF as well. */   

for (;;) {
    printf ("Enter y or n\n");
    c = getchar();
    switch (c) {
    case 'y': ...
        break;
    case 'n': ...
        break:
    case EOF:
        exit(0);
    }
}

Upvotes: 3

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