I wrote the following code in C to make a program which calculate the factorial of any number.
I want to add to my program some validation/error handling, such as preventing random characters, floats or negative values from being entered, so I used the isdigit function.
Unfortunately there is a hidden problem which I don't know how to solve. When I enter any input it considers it to be false (i.e. not a digit) even if it's a positive digit.
#include <stdio.h>
#include <ctype.h>
int main()
{
char choice;
unsigned long long int factorial=1;
int counter,number;
for(;;)
{
printf("Please , enter a positive integer number only : ");
scanf("%d",&number);
fflush(stdin);
if(isdigit(number))
{
for(counter=number;counter>1;counter--)
factorial*=counter;
printf("The factorial of number %d is %llu",number,factorial);
}
else
{
printf("\a\aError\n");
continue;
}
printf("\n1-Press c or C if you want to calculate the factorial of a new number\n2-Press any key if you want to exit the program\n ");
scanf("%c",&choice);
if(choice=='c'||choice=='C')
{
factorial=1;
system("cls");
continue;
}
else
return 0;
}
}
You are using isdigit wrong. Read its documentation to find out what it actually does.
You probably meant:
if ( number >= 0 && number <= 9 )
However you also need to check whether scanf succeeded or not. If they type in some words, then scanf("%d" fails and does not update number, so trying to access number in that case accesses an uninitialized variable. To deal with that you could either check the return value of scanf, or do:
int number = -1;
scanf("%d",&number);
because the value will be left unchanged if the input failed.
NB. Don't use fflush(stdin)
isdigit checks a single character if that's a decimal digit character.
But, your input could be say 25, multiple characters. So, I changed a portion:L
char input[30];
for(;;)
{
printf("Please , enter a positive integer number only : ");
scanf("%s",input);
if(isdigit(input[0]))
{
number = atoi(input);
for(counter=number;counter>1;counter--)
Keeping rest of your program snippet same.
Here, isdigit is used to check if the first character in input is a digit and therefore a valid candidate to be converted by atoi into an integer value number.
Related
I'm trying to create a C program to allow the user to input an integer number greater than 0, but if any other type is entered make the user try again until they enter an integer.
int minBet;
printf("Enter integer"\n);
while(scanf("%d",&minBet)!=1)
{
printf("Must be an integer value greater than 0\n");
scanf(" %d",&minBet);
}
When a non integer value is entered the printf statements loops infinitely. How can I solve this?
can only use stdio.h and NO global varables
If the input character doesn’t match the coversion, it’s left in the input stream to foul up the next read - you’ll have to get rid of it using getchar or fgetc.
while ( scanf( “%d”, &minBet ) < 1 )
{
getchar();
printf( “You entered a non-numeric value, try again: );
}
When you type let's say e, you type e and then press the ENTER key. So there are now 2 characters in the input buffer. scanf("%d") reads the e , but the newline character is still in the input buffer.
A simpler solution to your immediate problem is to add a getchar() after each scanf("%d"). This code will work .
#include <stdio.h>
#include <string.h>
int main(void)
{
int minBet;
printf("Enter integer \n");
while(scanf("%d",&minBet)!=1)
{
getchar();
printf("Must be an integer value greater than 0\n");
}
}
Additionally your code printf("Enter integer"\n); is wrong.It should be
printf("Enter integer \n");
I have been trying to add some experience in C to my experience with Python and started with a basic addition program. One thing that I'm trying to do is check if the input is a number or a character as seen here:
#include <stdio.h>
#include <ctype.h>
int main()
{
int n, sum=0,c,value;
printf("Enter the Number of Integers You Want to Add\n");
scanf("%d", &n);
if(isdigit(n))
{
printf("Enter %d Integers\n", n);
for(c=1; c<=n; c++)
{
scanf("%d", &value);
if(isalpha(value))
{
printf("ENTER INTEGER NOT CHARACTER\n");
break;
}
else
{
sum = sum + value;
}
}
printf("Sum of Entered Integers = %d\n",sum);
}
else
{
printf("ENTER INTEGER NOT CHARACTER\n");
break;
}
return 0;
}
Initially I had tried this using isalpha(), and the program worked fine when adding numbers but interpreted characters as zeros instead of printing the "not an integer" statement. However, now that I reworked it to use isdigit(), it does not recognize ANY input as an integer, whether or not it is. Is there something that I'm just doing wrong?
When you use scanf to read an integer, you get just that, an integer. (To read a single character, you need %c and a pointer-to-char).
When you use isdigit(), you need to supply the representation of that character (e.g. in ASCII, the character '0' has the representation 48, which is indeed its value as an integer). To recap:
isdigit(0) is false
isdigit(48) is true (for ASCII, ISO8859, UTF-8)
isdigit('0') is true (no matter the character set)
isdigit('0' + n) is true for integers n = 0 ... 9
PS: Not testing the return value from scanf is asking for trouble...
Neither isdigit nor isalpha work as you think they do. The intent of those library functions is to check whether a given code point, represented as an int, is within a subset of points defined by the standard to be digit characters or alpha characters.
You should be checking the results of your scanf calls rather than assuming they just work, and acting on those results accordingly. If you request an integer and one is successfully scanned, then it will tell you so. If that fails, your course of action is probably to consume the rest of the line (through newline or EOF) and possibly try again:
#include <stdio.h>
int main()
{
int n,value,sum=0;
printf("Enter the Number of Integers You Want to Add\n");
if (scanf("%d", &n) == 1 && n > 0)
{
printf("Enter %d Integers\n", n);
while (n--)
{
if (scanf("%d", &value) == 1)
{
sum = sum + value;
}
else
{
// consume the rest of the line. if not EOF, we
// loop around and try again, otherwise break.
while ((value = fgetc(stdin)) != EOF && value != '\n');
if (value == EOF)
break;
++n;
}
}
printf("Sum of Entered Integers = %d\n", sum);
}
return 0;
}
Properly done you should be able to enter valid integers beyond single digits (i.e. values > 10 or < 0), which the above allows.
The %d marker to scanf tells it to interpret the input as a number (more accurately, it indicates that the pointer in the arguments points to an integer type). It can't do anything but put an integer into that argument. If it can't interpret the input as a number, scanf stops scanning the input and returns immediately.
isdigit() evaluates its argument as a character code, as Jens points out above. However, scanf already turned the character code into a pure number.
From the scanf man page:
On success, the function returns the number of items of the argument list
successfully filled.
In your program, you are trying to read just one item from stdin, so scanf should return 1. So check for that and you'll know that it all worked out ok:
printf("Enter the Number of Integers You Want to Add\n");
while(scanf("%d", &n) != 1) {
printf("That's not a valid integer. Please try again.\n");
}
You cannot use isdigit() the way you are using it because you're already using scanf to convert the user input to an integer. If the user had not input an integer, scanf would have already failed.
Look at the man pages for all the C functions you are using, they will show you what the function expects and what the return values will be under different circumstances.
In the case of isdigit(), the input is expected to be an unsigned char representing an ASCII character. This can be a bit confusing because ASCII characters are in fact represented as a type of integer, and a string is an array of those. Unlike languages like Python which hide all that from you. But there is a big difference between the STRING of a number (array of characters that contain the characters of the digits of the number) and the INTEGER itself which is in a form the processor actually uses to do math with... (simplified explanation, but you get the idea).
Currently, I have a loop in my program that has the format:
#include<stdio.h>
int main()
{
int n;
while(1)
{
printf("Enter a positive number, n");
scanf("%d",&n);
if(n>0)
{
break;
}
}
}
My intention in using the if(n>0) statement was to exit the loop if and only if the user enters a positive integer. However, if the user types in the character "g", for example, the loop will still break, as the ASCII value will be interpreted. How do I form this loop so that it breaks just when the user enters a positive integer value for n?
Check the return value of scanf which returns the number of successful inputs read:
int rc = scanf("%d",&n);
if (rc==1 && n>0) {
...
}
I would suggest you to use fgets to read the input into a string and convert into integer using strtol as scanf is a poor choice for the reason said by #paddy.
I want to write a program where it prompts people to enter a set of integers separated by a space. The user should be able to enter any amount of integer. It will find the two smallest integer in the set and print it out. Printing the smallest number and then printing the second smallest. My question is how do I get the value of min1 to be the first integer they enter, other than a static one? When I did a test run all it printed was a space, why is that? Here is what I have so far:
Update:
I'm now trying this approach, but it just freeze after I enter an input such as 76 5 74 2.
#include <stdio.h>
int min1, min2;
int input;
int main(){
printf("Please enter some integer: ");
scanf("%d", &min1);
while(scanf("%d", &input) != 0){
min1=input;
}
printf("%d", min1);
return 0;
}
You should add \n in the end of the first printf, so it will not buffered.
Also, be care that you work with digits - not integers.
and for your question - just write min1=getchar();.
EDIT: some code that may do what that you want:
printf("Enter numbers. (other chars to end)\n");
int min,input;
scanf("%d",&min);
while (scanf("%d",&input))
if (input<min)
min=input;
printf("min: %d\n",min);
Maybe you need scanf("%d", &number); to read integers.
For your question, just call scanf to read the first number, or set up a flag to indicate if it's the first input.
Why did you got a space printed? Because %c prints characters not numbers, try %d.
But even after that you won't get the answer you are looking for. getchar() gets a character (go figure...) from the user input, and you are storing that character into a numeric value, for single digit numbers it would magically work since even as characters '9' > '8' > '7' > ... > '0', but you'll get the ascii value of the smallest number printed at the end.
You need two things:
Some way for the user to tell your program they are done entering numbers, so some kind of conditional statement
Some way to compare the numbers they have entered so another conditional statement comparing numbers
In sudocode, maybe something like:
while (user still wants to give numbers):
number = get user input
if number does not equal exit_case:
if number < current minimum number:
current minimum number = number
else:
break out of the while loop
print current minimum number
{
int a,b=1,min;
printf("Enter Number\n");
scanf("%d",&min);
while(b<10)
{
scanf("%d",&a);
if(min>a)
{
min=a;
}
b++;
}
printf("Smallest Num ::%d",min);
}
I'm trying to write a simple program where it ask user to enter a bunch of positive integers, and calculate the average of all the number entered. Program will terminate when user enter a non positive number like 0 or -1.
Here is my code. For some reason I get an error right when I try to enter the first input, can someone help?
#include <stdio.h>
int main()
{
int input=0, sum=0,average=0,i=0;
printf("Please enter positive numbers, enter 0 or -1 to end:\n");
scanf("%d",input);
while (input>0)
{
sum+=input;
i++;
scanf("%d",input);
}
average=sum/i;
printf("The average is %d",average);
}
You need to pass the address of the variable to scanf.Try this:
scanf("%d", &input);
^
Also see the C FAQ: Why doesn't the call scanf("%d", i) work?