How to control passes without stopping at scanf?

[bajajv]

Hi,

This is my code :

#include <iostream>
#include <stdio.h>
#include <stdlib.h>
 
const char arr1[] = {'+', '-', '*', '/', '>', '<'};
 
bool isOperator(char ch)
{
    bool res = false;
 
    if (ch == arr1[0])
        res = true;
    else if (ch == arr1[1])
        res = true;
    else if (ch == arr1[2])
        res = true;
    else if (ch == arr1[3])
        res = true;
    else if (ch == arr1[4])
        res = true;
    else if (ch == arr1[5])
        res = true;
 
    return res;
}
 
int main()
{
    char ch;
    do {
        //ch = '\0';
        printf("Enter char.\n");
        scanf("%c", &ch);
        printf("%s\n", (isOperator(ch) ? "true" : "false"));
    }while (ch != 'q');
    return 0;
}
 

When I run this code, it asks for char value, prints output, but next time it runs thru whole code again with some junk value in ch, without stopping at scanf().
I tried to put NULL in ch, but that didn't changed the flow.

Can you please check what is going wrong?

[horace1]

when using scanf() you enter the character followed by '\n' (<RETURN> character) to terminate the line. The scanf() reads the character but '\n' is left in the input stream. when you call scanf() the next time it reads the '\n' as the next charcater.
You need to remove the '\n' from the input stream and you can do this with a getchar(), e.g.

    do {
        //ch = '\0';
        printf("Enter char.\n");
        scanf("%c", &ch);
        printf("%s\n", (isOperator(ch) ? "true" : "false"));
        getchar();    // remove '\n'
    }while (ch != 'q');