Problem with Do while loop

Hi,

I am trying to write a function that promote users to enter an arithmetic operater, if they enter a wrong character i have to promote them again to enter it.

It work fine if they enter right arithmetic operator, but if they enter wrong character, the do while loop i have loop twise for no reason, i cant find the reason. Please help me out. ( more over number of loops increase if i put more than 1 charactor, if i put one wrong charactor its only loop twice but if i put 10 it look like 11 times.)

Code:

---

#include <stdio.h>

int main(void)
{
    char ope;
    do
    {
        printf("Enter an arithmetic operator (+, -, *, /): ");
        scanf("%c",&ope);
        if (ope=='+')
            printf("You have entered: %c\n",ope);
                else
                ;
    }
    while (ope!='+');
}

---

We want to absorb the enter key.

Code:

---

#include <stdio.h>

int main(void)
{
    char ope;
    do
    {
        printf("Enter an arithmetic operator (+, -, *, /): ");
        scanf("%c",&ope);
        getchar(); // absorb ENTER
       
        if (ope=='+')
            printf("You have entered: %c\n",ope);
                else
                ;
    }
    while (ope!='+');
}

---

The newbies love scanf.

Code:

---

#include <stdio.h>

int main() {
    int x;
    do {
        printf("Enter an arithmetic operator (+, -, *, /): ");
        x = getchar();
    } while (c != '+');
    printf("You entered %c\n", x);
}

---

That should work for you.

scanf("%c") will read, at most, one character. Any other characters you type will hang around until the next call to an input function. Even if you only type one character, you're still hitting enter, meaning a newline will get read the next time around, hence your extra looping.

The easiest way to fix this is to just use fgets() to read a line and look at the first character in the string.

my teacher told us to use a but i have no clue how to use it

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

I am not sure i am suppose to use getchar(); coz we never learn that in the class.


THank you for your help

I am unsure why it didn't work. scanf("%c\n", &myStr); didn't work for me either. I knew getchar() would work, so there it is.

Quote:

---

Originally Posted by prasdhy2008

my teacher told us to use a but i have no clue how to use it

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

I am not sure i am suppose to use getchar(); coz we never learn that in the class.


THank you for your help

---

Damn, really? I should teach C programming.

Babkockdood your solution works, but they cut marks ifwe use something we are not suppose to.

Quote:

---

Originally Posted by prasdhy2008

Babkockdood your solution works, but they cut marks ifwe use something we are not suppose to.

---

Replace x = getchar(); with scanf("%c", &x); then.

Quote:

---

Originally Posted by prasdhy2008

Babkockdood your solution works, but they cut marks ifwe use something we are not suppose to.

---

Then use scanf agian to grab the newline that is still in the input buffer right after your

Code:

---

scanf("%c",&ope);

---

Or change the scanf to get both at the same time.

*Note this will not work if you enter more then one character, or if you press enter first.
You would need to keep looping until you hit a newline to make sure you grab all the text the user enters.

Here is a function which clears you input buffer. Call this after your scanf function call.

Code:

---


void clear_buffer( void )
{
    int ch;
    while( ( ch = getchar()) != '\n' && ch != EOF );
}

---

ssharish