Why does my code skip over input from users? [closed] - c

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Closed 10 years ago.
So this is some code I have written, I am barley beginning on c so bear with me, my code makes sense to me but its not working properly, when am trying to say no to stop playing and display average it repeats the playing function.
Basically my program guesses the users number from 1-100 whatever number the user came up with. Here's some output that is wrong, just to give you an idea. The play game function is working fine but not the main.
Playing guess my number game
is your number 50 ?=
Great!
Play again? (y for yes n for no): is your number 50 ?=
Great!
Play again? (y for yes n for no): is your number 50 ?n
and so on i cant find where i went wrong any advice?
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <stdbool.h>
int playgame(void);
main() {
int numberofplays = 0;
float average = 0;
int numberguesses = 0;
printf("Playing guess my number game\n");
printf("-------------------------------\n");
bool play = true;
int xtry = 0;
int totaltries = 0;
char answer;
do {
xtry = playgame();
numberofplays++;
totaltries = totaltries + xtry;
printf("Play again? (y for yes n for no): ");
answer = getchar();
if(answer =='n')
play = false;
} while(play==true);
average = (float)(totaltries/numberofplays);
printf("average is %f tries per game\n",average);
return 0;
}
int playgame(void) {
int guessnumber = 50;
int xnumber = 25;
int count=0;
char x;
bool stillguessing = true;
while(stillguessing == true) {
printf("is your number %d ?", guessnumber);
x = getchar();
if(x=='=') {
count++;
printf("Great!\n");
stillguessing=false;
return count;
}
else if(x == '<') {
guessnumber = guessnumber - xnumber;
xnumber = xnumber/2;
if(xnumber<1) xnumber = 1;
count++;
}
else if (x == '>') {
guessnumber = guessnumber +xnumber;
xnumber = xnumber/2;
if(xnumber<1) xnumber = 1;
count++;
}
}
}

Answer 1

The function getchar pulls a character from the stream stdin.
The stream stdin contains everything that you have entered into the Standard Input device; in your case, this is the keyboard.
Now, when you respond to the computer's guess, you press two keys. You press = and then Enter.
Your code in playgame handles the =, but it leaves the Enter on stdin... thus, your next call to getchar pulls that.
What you need to do is to flush the stdin stream. You can't use fflush(stdin) for this, as fflush is for output streams.
Instead, you can use something like
void flushSTDIN() {
while ((ch = getchar()) != '\n' && ch != EOF);
}
to clear out any old newlines in the buffer, before you ask your question.
You should do this before all calls to getchar in your program.
So:
flushSTDIN();
printf("is your number %d ?", guessnumber);
x = getchar();

Answer 2

Your problem is that getchar() is consuming a single character from the input. However, the input stream always contains at least two characters when you enter a response: the character you enter (such as '=') and the newline (or enter) character that follows it.
This does not matter so much in the playgame() function (although all of the prompts are printed twice), but when you get to
answer = getchar();
this call to getchar() gets the newline that was left over from the previous character you typed.
How you fix this is a question of how you want to handle user input - whether you want to validate it, whether you want to be able to enter longer strings, etc.
In your case, the simplest solution is to replace your calls to getchar() with a loop that will discard whitespace.
I suggest doing the following:
Add the following line at (or near) the start of your program:
#include <ctype.h>
This provides the isspace() function that cleanly and portably checks if a character is whitespace.
Replace the line:
answer = getchar();
with:
while (isspace(answer = getchar()))
;
And similarly, replace
x = getchar();
with:
while (isspace(x = getchar()))
;
The single semicolon is a null statement - something (in this case nothing) has to go in the body of the loop.
Assigning to x/answer within a condition would often be frowned upon, but in this particular case it is the most idiomatic way of writing this.
Note that incorrect macro implementations of isspace() could cause issues by evaluating the call to getchar() multiple times