Random guessing game - bug

Question

I have a problem in this code when I enter a string, instead of integer. How do I check if the user has entred a character instead of integer? (I would like to put out a message to the user saying you should use numbers, not characters)

ALSO: if you find anything in this code I can improve, please help me! (I am new to C)

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main () {

    int secret, answer;

    srand((unsigned)time(NULL));

    secret = rand() % 10 + 1;

    do {
        printf ("Guess a number between 1 and 10");
        scanf ("%d",&answer);
        if (secret<answer) puts ("Guess a higher value");
        else if (secret>answer) puts ("Guess a lower value");
    } while (secret!=answer);

    puts ("Congratz!");
    return 0;
}

score 4 · Accepted Answer · answered Jun 15 '12 at 20:42

4

scanf returns the number of matches is finds. In your case it will return 1 if it readss a number. 0 if it can't read a number in:

if(scanf ("%d",&answer) != 1){
    puts("Please input a number");

    // Now read in the rest of stdin and throw it away.
    char ch;
    while ((ch = getchar()) != '\n' && ch != EOF);

    // Skip to the next iteration of the do while loop
    continue;
}

answered Jun 15 '12 at 20:42

Paul

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It should replace your scanf line – Paul Jun 15 '12 at 20:51
I figured it out. Thanks for not just making it a copy/paste, so I can learn more!!! – user1431627 Jun 15 '12 at 20:52
@user1431627 Also your if statements are backwards. You output that the number is lower if you guess too low, and you output that it is higher if you guess too high. – Paul Jun 15 '12 at 20:52
When I do that it only tells me to get a lower and lower number. – user1431627 Jun 15 '12 at 20:59
Yes. I did. I do not understand this actually. – user1431627 Jun 15 '12 at 21:01
But, how the heck should my code work if I have done a wrong if sentence? – user1431627 Jun 15 '12 at 21:05
Doing what I have already done works. Doing what you said I should it dose not work. I am confused. – user1431627 Jun 15 '12 at 21:09
if (secret>answer) puts ("The number is lower"); else if (secret – user1431627 Jun 15 '12 at 21:12
Oh, ok. Like this: if (secretanswer) puts ("Number is higher"); – user1431627 Jun 15 '12 at 21:17
Thank you SO MUCH for helping me! This is one of the first days of programming in C++. Btw, this code is cross-platform? – user1431627 Jun 15 '12 at 21:20
@user1431627 AFAIK it should be cross platform, as long as it is compiled for each platform it needs to be run on. That is `C` though, not `C++`. – Paul Jun 15 '12 at 21:56
Cool! Would you recommend me writing in C or C++? – user1431627 Jun 16 '12 at 08:41

score 3 · Answer 2 · answered Jun 15 '12 at 20:41

3

Read the input as a string (char[] and %s), check all characters are (isdigit()) digits (possibly allowing for a '+' or '-' as first character) and use atoi() to convert to int.

answered Jun 15 '12 at 20:41

hmjd

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score 0 · Answer 3 · answered Jun 15 '12 at 20:39

You should write a function that returns true if and only if every character in the string is a digit, and false otherwise.

char * in_str;
int answer;

...

sscanf("%s", in_str);

if (!is_number(in_str)) {
  printf("Please put in a number, not a letter");
} else {
  answer = atoi(in_str);
}

...

You need to implement the is_number function

score 0 · Answer 4 · answered Jun 15 '12 at 20:42

0

Since you can't assume that the user's input is an integer, have scanf() accept a string instead. Then try convert that string with strtol(); that will return 0 if the input was not an integer.

answered Jun 15 '12 at 20:42

chrisaycock

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score 0 · Answer 5 · answered Jun 15 '12 at 20:42

0

Read the input as a string with fgets and then use strtol to check the input. strtol contrary to atoi is able to do error checking.

answered Jun 15 '12 at 20:42

ouah

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Random guessing game - bug

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