How many ideas are there for converting uppercase and lowercase letters in C++?

C Introduction:

C is the inheritance of C language. It can not only perform procedural programming of C language, but also perform other tasks. Object-based programming characterized by abstract data types can also be used for object-oriented programming characterized by inheritance and polymorphism. While C is good at object-oriented programming, it can also perform process-based programming. Therefore, C is big or small in terms of the size of the problem it can adapt to.

C not only has the practical features of efficient computer operation, but is also committed to improving the programming quality of large-scale programs and the problem description capabilities of programming languages.

C There are several ideas for converting uppercase and lowercase letters:

Idea 1. Convert according to the ASCII table of letters:

As can be seen from the table, the difference between the corresponding uppercase and lowercase letters is 32, from which the following programming ideas can be derived:

Program 1.1

#include <iostream>
using namespace std;
int main()
{
	char a[20];
	int i = 0;
	cout<<"请输入一串字符:\n";
	cin>>a;
	for(;a[i];i++)
	{
		if(a[i] >= &#39;a&#39;&&a[i] <= &#39;z&#39;)
            a[i] -= 32;
		else if(a[i] >= &#39;A&#39;&&a[i] <= &#39;Z&#39;)
            a[i] += 32;
	}
	for(i = 0;a[i];i++)
		cout<<a[i];
	cout<<endl;
	system("pause");
	return 0;
}

Program 1. 2

#include <iostream>
using namespace std;
void main(void)
{
    char i;
    cout<<"Input,&#39;#&#39;for an end: "<<endl;
    while(1)
    {
        cin >> i;
        if ((i>=65)&&(i<=90))
        {
            i=i+32;
            cout << i;
        }
        else if((i>=97)&&(i<=122))
        {
            i=i-32;
            cout << i;
        }
        else
            cout << (int)i;
        if(i==&#39;#&#39;)
            break;
    }
}

Idea 2: Using the uppercase and lowercase letter conversion function, the following programming ideas can be derived from this:

Program 2.1 Simple version

#include <iostream>
using namespace std;
int main()
{
    cout<<(char)toupper(97)<<&#39;\n&#39;;
    cout<<(char)toupper(&#39;a&#39;)<<&#39;\n&#39;;
    cout<<(char)tolower(66)<<&#39;\n&#39;;
    cout<<(char)tolower(&#39;B&#39;)<<&#39;\n&#39;;
    return 0;
}

Program 2.2 Utilize functions strupr, strlwr

#include<iostream>
#include<string>
using namespace std;
int main()
{
    //声明字符数组
    char str[80],*p;
    int i;
    //转换字符串中的小写为大写
    cout<<"将字符串中的小写字母转换为大写"<<endl;
    cout<<"请输入原字符串："<<endl;
    cin>>str;
    p=strupr(str);
    cout<<"p:"<<p<<endl;
    cout<<"string:"<<str<<endl;
    cout<<"___________________"<<endl;
    //转换字符串中的大写为小写
    cout<<"将字符串中的大写字母转换为小写"<<endl;
    cout<<"请输入原字符串："<<endl;
    cin>>str;
    p=strlwr(str);
    cout<<"p:"<<p<<endl;
    cout<<"string:"<<str<<endl;
    cout<<"___________________"<<endl;
system("pause");
return 0;
 
}

Program 2.3 Utilize functions toupper, tolower

#include<iostream>
#include<cctype>
#include<vector>
using namespace std;
int main()
{
    vector<char> vch;
    int n;
    char elem;
    cout<<"请输入大小写字符的个数：";
    cin>>n;
    cout<<"请输入"<<n<<"个大小写字符：";
    for(int i = 0;i<n;++i)
    {
        cin>>elem;
        vch.push_back(elem);
    }
    vector<char>::iterator it = vch.begin();
    for(it;it != vch.end();++it)
 
    {
       if(*it >= &#39;a&#39;&&(*it) <=&#39;z&#39;)
            *it = toupper(*it);
        else if(*it >= &#39;A&#39;&& (*it) <= &#39;Z&#39;)
            *it = tolower(*it);
    }
    cout<<"大小写转化之后的结果：";
    vector<char>::iterator itera = vch.begin();
    for(itera;itera != vch.end();++itera)
        cout<<*itera;
    cout<<endl;
    return 0;
}

Program 2.4 Use transform with tolower and toupper to combine

#include<iostream>
#include<algorithm>
#include<string>
#include<cctype>
using namespace std;
int main()
{
    cout<<"请输入一个全部大写的字符串：";
    string str;
    cin>>str;
    ///转小写
    transform(str.begin(),str.end(),str.begin(),tolower);
    ///transform(wstr.begin(), wstr.end(), wstr.begin(), towlower);
    cout<<"转化为小写后为："<<str<<endl;
    ///转大写
    cout<<"请再输入一个全部小写的字符串：";
    string s;
    cin>>s;
    transform(s.begin(), s.end(), s.begin(), toupper);
    ///transform(wstr.begin(), wstr.end(), wstr.begin(), towupper);
    cout<<"转化为大写后为："<<s;
    wstring wstr =L"Abc";
    transform(wstr.begin(), wstr.end(), wstr.begin(), towupper);
    cout<<wstr;
    return 0;
}

Program 2.5 is written as a convert function, using |= and &= to transform

#include <iostream>
#include <cassert>
using namespace std;
char* convert(char *src)
{
    char *p = src;
    assert(p != NULL);
    while(*p)
    {
        if (&#39;A&#39; <= *p && *p < &#39;Z&#39;)
            *p |= 0x20;
        else if (&#39;a&#39; <= *p && *p < &#39;z&#39;)
            *p &= ~0x20;
        p++;
    }
    return src;
}
int main()
{
    char src;
    cin>>src;
    convert(&src);
    cout<<src;
    return 0;
}

Recommended tutorial: "C Language Tutorial"

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