integer test.cpp

用来测试输入的是数字还是字符串

/*
 program name: Integer Test
 Sometimes we need a way to test the user input to know if it is an integer, i have
 seen many algorythm for doing this,but a lot of them are incomplete since they only check
 to see if the input contain the numeric values from 0 to 9 if so it is said that the input 
 is a number.Here you will fine a more precise way to test the user input for knowing if it 
 is an integer.

 If you like this code,please vote for it !


 written by Gonzales Cenelia.
*/

#include <stdio.h>
#include <string.h>
#include <ctype.h>

// This is the function that makes the integer test
bool IsInteger( char *number )
{
   int len = strlen( number );
   bool isnumber = true;
   int i = 0;

   if( len == 0 || len > 9 ) // if the user did not enter an input
   {                         // or if the input is too big to be
	   return false;         // a "long" value.
   }

   while( i < len && isnumber ) // scanning the the input
   {
       if( isdigit( number[i] ) == 0 ) // check if there is a none digit character in the input
       {
            if( number[i] == '+' || number[i] == '-' ) // if so we verify if it is "+" or "-"
            {
                if(  i + 1 > len - 1 || i - 1 >= 0 ) // check the position of "+" or "-"
                {                                    // this signs could only be infront of
                   isnumber = false;                 // the number,no where else.
                }
            }
            if( number[i] != '+' && number[i] != '-' ) // if it's not "+" or "-" than
            {                                          // the expression is not a number
                isnumber = false;
            }
       }
       i++;
   }

   return isnumber;
}

void main()
{
    char number[20]; // buffer for storing number
    
    printf("Enter a number: "); // geting a number from the user
    gets(number);
    
	if( IsInteger( number ) == false ) // testing the input number
	{
       printf("This is not an integer.\nOr maybe this expression is too big "
	          "to be tested.\n");
	}
    else
	{
       printf("Thanks for entering an integer !\n");
	}

	// Since the number is stored as a string,if you need to convert
	// it to numeric value, you can use something like 
	// "long numvalue = atol(number)"
	// you might start testing the program with the following numbers:
	// 14563,35.1223,-6853,+655
}