#include<stdio.h>
#include<conio.h>
#include<math.h>

void main()
{

    int i=0,f=0,s=0;
    char arr[80];

    printf("Enter any input string terminated by $:");
    scanf("%s",arr);

    while(arr[i]!='$' && f==0)
    {
        switch(s)
        {
            case 0:
                if(arr[i] >='0' && arr[i] <='9')
                {
                    s=1;
                    i++;
                }
                else

                    f=1;
                    break;

            case 1:
                 if(arr[i] >='0' && arr[i] <='9')
                 i++;
                 elseif(arr[i]=='.')
                 {
                 s=2;
                 i++;
                 }
                 else
                 f=1;
                 break;

            case 2:
                if(arr[i] >='0' && arr[i] <='9')
                {
                    s=3;
                    i++;
                }
                else
                    f=1;
                    break;
              case 3:
                 if(arr[i] >='0' && arr[i] <='9')
                 i++;
                 elseif(arr[i]=='E' || 'e')
                 {
                 s=4;
                 i++;
                 }
                 else
                 f=1;
                 break;
            case 4:
                if(arr[i] == '+' || arr[i] == '-')
                {
                s=5;
                i++;
                }
                else
                f=1;
                break;

            case 5: if(arr[i] >='0' && arr[i] <='9')
                i++;
                else
                f=1;
                break;

        }

    }
      if(f==1)
    printf("\nInvalid String !");
      else
    printf("String is Valid ");

getch();
}




OUTPUT
***********
Enter any input string terminated by $:12.12E+12$
String is Valid

Enter any input string terminated by $:10.12E15$
Invalid String !




[/Code]