Thread: int value of char

I have written a function which receives a char variable and checks it's int value for certain restrictions, but when I try to compare it with -1 it doesnt work and I don't know why.

can anyone help me please?




void INIT(int poly[]){
int i=-1, n;
const MAX=10;
char temp, power;

for (n=1;n<=MAX;n++){ /* stops after 9 good entries */
printf("Enter power and coefficient\n");
printf("power of %d stops receiving the polynomial\n",-1);

scanf("%s ",&power);

int rank=(power-'0');
if(rank== -1) /* stops "for" loop if power= -1 */
break;

if(rank==i){ /* cheks the power hasn't been entered twice */
printf("current power already entered\n");
printf("begin again\n");
return;
}

scanf("%s",&temp);
int num=(temp-'0'); /* checks that the entry is legal
if it's not it stops the function*/
if(rank>=0 && (rank<=9))
if(num>=0 &&(num<=999))
poly[rank]=num;

if(rank<0 && (rank>9)){
printf("wrong entry please start again\n");
return;
}

rank=i;
} /* end of receiving polynomial */

I have written a function which receives a char variable and checks it's int value for certain restrictions, but when I try to compare it with -1 it doesnt work and I don't know why.

you cant be sure of the signedness of a char so if you need to check it for a negative value then declare it as signed

signed char temp, power;

I have to receive anything frm the user and when I get garbage the function should stop.
that's why I've used "scanf %s".

It does ignore the garbage but it doesn;t stop untill it receives 9 valid entries.

Originally posted by Hammer
Don't be sad, it's all fun learning C

Usualy I'd agree with you.

Thaks.

I'm going to try something like that.
Atleast now I know how to do it.

I hope it will work

Originally posted by Hammer
Here's a sample program showing how to validate user input. It asks for a number between 0 and 10, or -1 to exit. Anything else is considered to be an error.

Hopefully, this may help your understanding.

Code:

#include <stdio.h>
#define MAX 10

int main(void)
{
	int num1;
	
	for (;;)
	{
		printf ("Please enter an int between 0 and %d, or -1 to exit\n", MAX);
		if (scanf("%d", &num1) == 1)
		{
			if (num1 == -1)
				break;
			if (num1 >= 0 && num1 <= MAX)
				printf("You entered %d\n", num1);
			else
				printf("%d is out of range\n", num1);
		}
		else
		{
			printf("That was not a number\n");
			while (getchar() != '\n'); /* Eat duff character from buffer */
		}
	}
	return (0);
}

I changed my function and it works great


Thanks !!! (I'm so happy)

/*
as you wrote "but when I try to compare it with -1 it
doesnt work and I don't know why."
going through your programm there are certain things which
would be best to bring to your notice
1.if(rank<0 && (rank>9))
now this condition would never be satisfactory
why
because rank can never be <0 and at the same time >9
both are going opposite directions <0 is going
towards -1,-2 and so on whereas >9 is becoming
10,11 and so on; therefore || should be used like
if(rank<0 || (rank>9))//now this is ALLRIGHT
because either rank could be <0 or >9;
in one other of your statements
if(rank>=0 && (rank<=9))//using && is ok
because yes rank can be >=0 and at the same time
<=9 why because 9 is >=0 and 0 is <=9 both would at
some stage meet eachother >=0 is being 1,2 and so
on whereas <=9 is being 8,7 so it is evident why your
using && in one statement is correct
and wrong in other;
2. why do you use %s in scanf when you declared power
as
char power?
althou it does not generate errors,
but scrutinize it and you would find in power the value
stored would be of one byte only wheather you use
%s or %c;allright u would say no it wont be like that;
then see you wrote scanf("%s ",&power);
the above statement when executed would actually
make the scanf to work twice that is if you hit A and
then hit ENTER still you will have to hit some other key
and then ENTER again;all this because you kept space
between"%s " and not "%s"; but even then the
character which is hit first would only be
recorded and not the second one in this
case recorded charater would be A;
scanf("%s",&power);//now the scanf will work
normall as it should
that is only once when you will hit ENTER it would
teminate but still even if you hit ABC and then hit enter
only A is the recorded character BC went unrecognised;
so my suggestion is use only %c when it is just char
power;if you want to store multiple values in power
then make it an array;then using %s would
make sense;
3. you have already in the begining of the function made
int i=-1;
but still you write these two if statements together;
if(rank== -1) // stops "for" loop if power= -1
{
printf(" i am breaking");
break;
}
if(rank==i)
{ // cheks the power hasn't been entered
twice
printf("current power already
entered\n");
printf("begin again\n");
return;
}
//////////
have a look above once more and try to comprehend
what is the diffrence
between -1 and i ?when you made i=-1 in the
beginging!
so if the condition is satisfied for rank==-1
the control will go out of loop allready and will never
reach
the immediate if statement which is if(rank==i).so this if
statement is only occupying the space of your
programm
and nothing else. only first if statement
that is if(rank==-1) would do the job;
4.from above function it is evedinet that rank would
only be -1 when
someone hits '/' or ther maybe some other way
too.but with what exactly do you want to compare -1
with? is it with rank or num or temp or with
something else? then maybe your solution might
appear
please tell this much.
5.i am just a student and you seem to be some
professional
so please dont mind if i am wrong somewhere please
correct me
i my self need guidence of your esteemed self;
6.this is how i tried to understand your function

#include<includes.c>
void INIT(int poly[])
{
int i=-1, n;
const MAX=10;
char temp,power
int rank;int num;
for (n=1;n<=MAX;n++)
{ // stops after 9 good entries
printf("Enter power and coefficient\n");
printf("power of %d stops receiving the
polynomial\n",-1);
fflush(stdin);
scanf("%s",&power);
fflush(stdin);
printf("\n%c=power\n",power);//just a check
rank=(power-'0');
printf("rank: %d\n",rank);//just acheck
if(rank== -1) // stops "for" loop if power= -1
{
printf(" i am breaking");//wanted to make sure if control reaches here
break;
}
if(rank==i)
{// cheks the power hasn't been entered twice
printf("current power already entered\n");
printf("begin again\n");
return;
}

fflush(stdin);
printf("value for temp ");//just a check
scanf("%s",&temp);
fflush(stdin);
printf("\ntemp=%c",temp);//just a check
num=(temp-'0'); // checks that the entry is legal
//if it's not it stops the function
printf("\nnum:-%d\n",num);//just a check
if(rank>=0 && (rank<=9))
{
if(num>=0 &&(num<=999))
{
poly[rank]=num;
printf("poly[%d]=%d\n",rank,poly[rank]);//just a check
}
}
if(rank<0 && (rank>9))//instead of && it should be ||
{
printf("wrong entry please start again\n");
return;
}

rank=i;
printf("rank=%d n=%d",rank,n);//just a check;
} // end of receiving polynomial

}

void main()//to make your fuction work i made this
//main from where i called it;
{
char *one;
one=(char *) malloc(sizeof("hello"));
one="hello";
clrscr();
printf("%s\n",one);//checking if hello has been inserted in one or not;
INIT((int *)one);//and passed this one;
getch();

}
*/

Wow,
I'm impresed.
I'm a student too and at the very begining of Cprog.
That's why I ask so many Q.

I did make some stupid mistakes but now after much help
I got it right, it's pretty long but here goes:

One more thing:
I only used i= -1 so when first I check (power==i)
it wont stop running (I can use power 0).
After that at the end of the loop I assign "i=power;"
so next time if power was already entered it will stop running.

************************************************** **

void INIT(int poly[]){
int i=-1,n;
int temp,num,power;
const MAX=9;

/* checks that the entry is legal if it's not it stops function*/
for (n=MAX;n>0;n--) /* stops after 9 good entries */
{
printf("Enter power\n");
printf ("Please enter an int between 0 and %d, or -1 to exit\n", MAX);

if (scanf("%d", &power) == 1)
{
if (power == -1)
break;
if (power >= 0 && power <= MAX)
printf("You entered %d\n", power);
else
{
printf("%d is out of range\n", power);
return;
}
}
else
{
printf("That was not a number\n");
return;
while (getchar() != '\n');
}

if(power==i||(poly[power])) /* cheks that the power hasn't been entered twice */
{
printf("current power already entered\n");
return;
}
printf("Enter coefficient\n");
printf("Please enter an int between %d and %d\n",-999,999);

if (scanf("%d", &temp) == 1)
{
if (temp >= -999 && temp <= 999)
printf("You entered %d\n", temp);
else
{
printf("%d is out of range\n", temp);
return;
}
}
else
{
printf("That was not a number\n");
return;
while (getchar() != '\n');
}

poly[power]=temp;
i=power;

} /* end of receiving polynomial */

/* next part prints the polynomial as received */

i=9;
num=poly[i];
printf("%dx%c%d",num,'^',i);

for(i=8;i>=0;i--)
{
num=poly[i];
if(num>=0)
printf("%c%dx%c%d",'+',num,'^',i);
else
printf("%dx%c%d",num,'^',i);
}
} /* end of function */