C++：如何在没有 ctype 函数的情况下将小写转换为大写，反之亦然？

Question

int main(){
char text[500];
int j,h,op;
char b[]=" abcdefghijklmnopqrstuvwxyz";
char a[]=" ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 
cout<<"insert text:";fflush(stdin);gets(texto); 
        system("cls");
            cout<<"1-Minus to Mayus"<<endl;
            cout<<"2-Mayus to Minus"<<endl;
        cin>>op;
    system("cls");
    if (op==1)
                    {
                                j=0;
                                h=0;
                                while(j<28){

                                    if(text[h]==b[j]){
                                        text[h]=a[j];
                                        h++;
                                        j=0;
                                    }
                                    j++;
                                }
                                cout<<text<<endl;
                                system("pause");
                    }
                    else if (op==2)
                    {
                                j=0; 
                                h=0;
                                while(j<28){

                                    if(text[h]==a[j]){
                                        text[h]=b[j];
                                        h++;
                                        j=0;
                                    }
                                    j++;        
                                }
                                cout<<text<<endl;
                                system("pause");
                }
            }

This code works just with a single world (until the first space), I want it to run with a whole sentence or even a paragraph.I hope that you could understand the logic of lower to upper function in the main()

Answer 1

If it is the case that you do not want this code to depend on the values of an ASCII table (although this could make your life much easier), following the spirit of your interestingly fashioned code, a function to convert letters to lowercase could be implemented as such:

const char LOWERCASES[] = " abcdefghijklmnopqrstuvwxyz";
const char CAPITALS[] = " ABCDEFGHIJKLMNOPQRSTUVWXYZ";

void toLowerCase(string &s) {
    for (unsigned int i = 0; i < s.size(); ++i) {
        for (unsigned int l = 0; l < 27; ++i) {
            if (s[i] == CAPITALS[l]) {
                s[i] = LOWERCASES[i];
                break;
            }
        }
    }       
}

Answer 2

Try this

int main(){

int ss,T;

char text[100]; 

cout<<"Insert text ";gets(text);
T=tam(texto);
    cout<<"1)Menu "<<endl;
    cout<<"2)Upercase "<<endl;
    cout<<"3)LowerCase "<<endl;
    cout<<"4)Random"<<endl;cin>>ss;

switch(ss){

    case 2:
            for(int i=0 ; i<T ; i++){
                if(text[i]>=97 && text[i]<=122)
                    text[i]=int(text[i])-32;
            }
            cout<<text<<endl;

    break;  

    case 3:
            for(int i=0 ; i<T ; i++){
                if(text[i]>=65 && text[i]<=90)
                    text[i]=int(text[i])+32;
            }
            cout<<text<<endl;

    break;


    case 4:
            for(int i=0 ; i<T ; i++){
                if(text[i]>=97 && text[i]<=122)
                    text[i]=int(text[i])-32;
                else
                    text[i]=int(text[i])+32;    
            }

            cout<<text<<endl;

    break;
}

}