I want the code to check input in command line is integer. i.e. 10b is not valid. I tried isdigit() but is not working? Thanks in advance.
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
int main(int argc, string argv[])
{
if (argc == 2)
{
int key = atoi(argv[1]);
if (isdigit(key))
{
printf("Success\n\%i\n", key);
exit(0);
}
}
printf("Usage: ./caesar key\n");
return 1;
}
Function isDigit checks if a single character is a digit, i.e. in the range between '0'..'9'. To check if a string is a number, I'd suggest to use function strtol.
long strtol(const char *str, char **str_end, int base ) converts a string str to an integral number and also sets the pointer str_end to the first character that took not part in the conversion any more. If you require that no characters must follow your number, then str_end must point to the string's end, i.e. to string termination character '\0':
#include <stdio.h>
#include <stdlib.h>
int isNumber(const char* str) {
if (!str || *str=='\0') { // NULL str or empty str: not a number
return 0;
}
char* endOfNum;
strtol(str,&endOfNum,10);
if (*endOfNum == '\0') { // string is at its end; everything in it was a valid part of the number
return 1;
} else {
return 0; // something that is not part of a number followed.
}
}
int main() {
const char* vals[] = {
"10b",
"-123",
"134 ",
" 345",
"",
NULL
};
for (int i=0; vals[i]; i++) {
printf("testing '%s': %d\n", vals[i], isNumber(vals[i]));
}
}
Output:
testing '10b': 0
testing '-123': 1
testing '134 ': 0
testing ' 345': 1
testing '': 0
Adapt the meaning of corner cases like empty strings or NULL-strings to your needs.
The isdigit function checks whether a single character represents a single digit. (numbers − 0 1 2 3 4 5 6 7 8 9).
In order to check if a string is an integer you could use a function like that. It will
bool isNumber(char number[])
{
int i = 0;
// only if you need to handle negative numbers
if (number[0] == '-')
i = 1;
for (; number[i] != 0; i++)
{
if (!isdigit(number[i]))
return false;
}
return true;
}
'+' and use isdigit((unsigned char) number[i]) for correct functionality when number[i] < 0.My first thought would be to use something like:
int inputvalue = 0;
if (sscanf(argv[i], "%d", &inputvalue) == 1)
{
// it's ok....
}
else
{
// not an integer!
}
or something like that. See http://www.cplusplus.com/reference/cstdio/sscanf/
'b' mentioned in the question.
sscanf has undefined behavior on numeric overflow. If the input is 999999999999999999999999999, anything can happen.
atoidoes no error checking. And the correct declaration isint main(int argc, char *argv[]); the<cs50.h>header's definitiontypedef char *string;is a really bad idea. (A pointer is not a string.)"1234567890123456789012345678901234567890"an integer. Math-wise it is, but certainly will not fit in anintor commonlong long.