Asking for input again with do while loop in c - c

Question

I am trying to have the user type in a number between 1 and 8 to print out stuff on screen (height), if the number is lower than 1 or higher than 8 I would like for the program to prompt again for an input instead of it quitting out and say "invalid". I know I have to set it up with do on top and when on the bottom in C, my question is how would I go about it when I have 2 possible outcomes, i.e. too low or too high?
do {
int height = get_int(Height: ");
if (height < 1)
~ ~printf("invalid");
else if (height > 8)
~ ~printf("invalid");
} when(???????)
printf("valid")

Answer 1

The key is Logical OR operator (||) in logical operator.
A logical operator would :
treats its operands as boolean values
treats a non-zero value operand as true
treats a zero value operand as false
operates the boolean algebra on its operands
returns the boolean algebra result
returns 1 for true boolean result
returns 0 for false boolean result
The Logical OR operator (||) :
lhs || rhs
Here, lhs and rhs are the 2 operands of OR(||) operator
The OR operator returns 1 if any of the following conditions is true:
only lhs is true
only rhs is true
both lhs and rhs are true
In other words, the boolean algebra OR result is true if either lhs or rhs is true.
In your example, there are 2 conditions :
height is less than 1
height is larger than 8
if either of them is true, then the result is true (the loop will continue), so the expression in this example would be :
int height; /* move height outside the loop so it can be used in do-while condition */
do {
height = get_int();
if (height < 1)
printf("invalid\n");
else if (height > 8)
printf("invalid\n");
} while(height < 1 || height > 8);
printf("valid\n");
Furthermore, since we have already done the logical condition in the loop, we can just add a flag variable instead:
int flag; /* record the boolean result */
do {
int height = get_int();
if (height < 1) {
printf("invalid\n");
flag = 1;
} else if (height > 8) {
printf("invalid\n");
flag = 1;
} else {
flag = 0; /* !(height < 1 || height > 8) */
}
} while(flag);
printf("valid\n");

Answer 2

Try this to see if it works for you.
If not, leave a comment to tell me what you really want.
#include <stdio.h>
int main()
{
int height = 0;
while (height < 1 || height > 8) {
scanf("%d", &height);
if (height >= 1 && height <= 8) {
break;
} else {
printf("Invalid, please try again.\n");
}
}
printf("Valid.\n");
return 0;
}

Answer 3

A simple way of checking if the user has made an invalid choice would be to use a simple Boolean variable and set it to "false" when an invalid choice is made.
I have modified your own example code to include what I mean here:
bool valid = true;
do {
valid = true; //reset valid to true at the beginning of the loop, otherwise it will remain false when the loop runs again
int height = get_int("Height: ");
if (height < 1)
valid = false; //set valid to false when an invalid choice is made
else if (height > 8)
valid = false; //set valid to false when an invalid choice is made
} while (!valid) //if valid is not true ( or ==false), repeat. If valid is true or not equal to false, don't repeat and continue to the print statement below.
print("valid");
Please note that I used the same get_int function you provided in your post. I am not aware of this function. For ways of reading integers (for example scanf) see other answers in this thread.

Answer 4

I hope this helps you.
#include <stdio.h>
#include <stdlib.h>
int main() {
int num;
do {
printf("Enter 0 to quit\n");
printf("Print Enter number between 1 and 8\n");
scanf("%d",&num);
if (num > 8) {
printf("Number to high\n");
} else if (num < 0) {
printf("Number to low\n");
}
if (num == 0) {
printf("You quit the program goodby\n");
} else {
printf("Number within range\n");
}
} while(num != -0);
return 0;
}