程序代码：

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

int main()
{
    char num[6];
    int i,a=0,b=0;

    printf("Please input your ID number:\n(including two letters & 4 digits)\n");

    for (i=0; i<6; i++)
        scanf("%c", &num[i]);

    for (i=0; i<2; i++)
    {
        if(isalpha(num[i]))
            a++;
    }

    for (i=2; i<6; i++)
    {
        if(isdigit(num[i]))
            b++;
    }
    if (a!=2 || b!=4 )
        printf("Wrong!");
    else
        printf("Please choose an option:\n(1) Start a test\n(2) Check scores\n(3) Exit\n");

    return 0;
}

程序代码：

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <ctype.h>

int main()
{
    int i, a=0, b=0, option;
    char no[6];
    printf( "This program will help elementary school pupils practice math.\n" );
    printf( "Please input your ID number:\n(including two letters and four digits)\n" );
    
    /*Check the ID number*/
    
    for (i=0; i<6; i++) 
    scanf("%c", no[i]);
    for (i=0; i<2; i++)
    {
        if (isalpha (no[i]))
        a++;
    }
    for (i=2; i<6; i++)
    {
        if (isdigit (no[i]))
        b++;
    }
    if (a !=2 || b !=4)
    printf("PLease check your ID number and run again.\n");
    
    /*start the program*/
    
    else 
    {
        printf("PLease input a number less than 4 to choose an option:\n(1)Start a test\n(2)Check scores\n(3)Exit");
        scanf("%d",&option);
        do 
        {
            printf("Oh, please choose it again");
        }
        while (option<4);
        
        switch(option)
        {
            case 1: printf("yeah");
                break;
            case 2: printf("wrong");
            break;
            case 3: return 0;
            break;
        }
        
    }
    
    return 0; 
}