Header file ctype H (detailed)

1、ctype.h The function in

2、 Code understanding

#include<iostream>
#include<algorithm>
#include<ctype.h>
#include<cstring>
using namespace std;

int main()
{
    

    char str[1007];
    cin>>str;
    int len = strlen(str);


    for(int i=0;i<len; i++)
    {
    
        if(isalnum(str[i]))   // Judge whether it is a number or a letter 
        {
    
            if(isdigit(str[i]))  // Judge whether it's a number 
            {
    
                cout<<" It's a number ："<<str[i]<<endl;
            }

            if(isalpha(str[i]))  // Decide if it's a letter 
            {
    
                if(islower(str[i])) // Determine if it's lowercase 
                {
    
                    cout<<" Change lowercase to uppercase ："<<char(toupper(str[i]))<<endl;// Change lowercase letters to uppercase letters 
                }

                if(isupper(str[i]))   // Decide if it's a capital letter 
                {
    
                    cout<<" Change uppercase to lowercase ："<<char(tolower(str[i]))<<endl;// Change uppercase letters to lowercase letters 
                }

            }
        }
        if(!isalnum(str[i]))
        {
    
            cout<<" It's not a letter or a number ："<<str[i]<<endl;
        }

    }



    return 0;
}

Running results ：

Other functions can be used by yourself ~