在字符串向量中测试int

Question

I'm writing a program where I need to get a line of input that consists of a letter and two numbers with spaces in between.Let's say,something like "I 5 6".

I use std::getline to get input as a string so there wouldn't be any problems with the blank space and then a for loop to browse through the individual characters in the string. I need a certain condition to execute only if the 2nd and 3rd characters(3rd and 5th counting the blanks) are numbers.

How can I test if a character at a certain position in a string is an int?

Answer 1

For your purpose, I would put the line into an std::istringstream and use the normal stream extraction operator to get the values from it.

Perhaps something like

char c;
int i1, i2;

std::istringstream oss(line);  // line is the std::string you read into with std::getline

if (oss >> c >> i1 >> i2)
{
    // All read perfectly fine
}
else
{
    // There was an error parsing the input
}

Answer 2

You can use isalpha . Here is an example:

/* isalpha example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="C++";
  while (str[i])
  {
    if (isalpha(str[i])) printf ("character %c is alphabetic\n",str[i]);
    else printf ("character %c is not alphabetic\n",str[i]);
    i++;
  }
  return 0;
}

isalpha Checks whether c is an alphabetic letter. http://www.cplusplus.com/reference/cctype/isalpha/

The output will be:

character C is alphabetic character + is not alphabetic character + is not alphabetic

And for digits use isdigit :

/* isdigit example */
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main ()
{
  char str[]="1776ad";
  int year;
  if (isdigit(str[0]))
  {
    year = atoi (str);
    printf ("The year that followed %d was %d.\n",year,year+1);
  }
  return 0;
}

The output will be:

The year that followed 1776 was 1777

isdigit Checks whether c is a decimal digit character. http://www.cplusplus.com/reference/cctype/isdigit/

Answer 3

There is a function isdigit() for it:

To check 2nd and 3rd characters of a string s you can use this code:

if (isdigit(s[2]) && isdigit(s[3]))
{
  // both characters are digits
}

But in your case ( s == "I 5 6" ) it seems that you need to check s[2] and s[4] .