{"post":"

In cases, when the whole string needs to be converted to upper case or lower case, we can use these methods for the conversion:

Changing the ASCII code of all characters.
Using functions: toupper and tolower

Another interesting way would be to convert uppercase letters to lower case letters and lower one to upper. It is also given below, as an extra segment.

Method 1: Changing the ASCII code of all characters

Logic:

The difference between the first character of uppercase and ASCII code of lower case character is 32, We add 32 to upper case letters in order to convert them to lower case, and we subtract 32 from lower case letters to convert them to upper case.

Algorithm to convert uppercase to lowercase:

Check if the character is between A and Z i.e. it is a capital letter,
If the character is a capital, we add 32 to it.
Else, the character is already in lower case. Do nothing.

Algorithm for lowercase to uppercase:

Check if the character is between ‘a’ and ‘z’ i.e. it is a lower case letter.
If the character is a lower case letter, we subtract 32 from it.
Else, the character is already in upper case. Do nothing.

Code:

#include <iostream>\nusing namespace std;\n\nvoid lower_string(string str)\n{\n\tfor(int i=0;str[i]!='\\0';i++)\n\t{\n\t\tif (str[i] >= 'A' && str[i] <= 'Z')    //checking for uppercase characters\n\t\t\tstr[i] = str[i] + 32;         //converting uppercase to lowercase\n\t}\n\tcout<<\"\\n The string in lower case: \"<< str;\n}\n\nvoid upper_string(string str)\n{\n\tfor(int i=0;str[i]!='\\0';i++)\n\t{\n\t\tif (str[i] >= 'a' && str[i] <= 'z')   //checking for lowercase characters\n\t\t\tstr[i] = str[i] - 32;        //converting lowercase to uppercase  \n\t}\n\tcout<<\"\\n The string in upper case: \"<< str;\n}\n\nint main()\n{\n\tstring str;\n    cout<<\"Enter the string \";\n    getline(cin,str);\n    lower_string(str);       //function call to convert to lowercase\n\tupper_string(str);   //function call to convert to uppercase\n\treturn 0;\n}\n

Output:

Enter the string Hola Amigos!\nThe string in lower case: hola amigos!\nThe string in upper case: HOLA AMIGOS!\n

Method 2 : Using toupper() and tolower()

Logic:

The predefined method toupper() and tolower() takes an integer as input.

It returns the same character converted, according to the upper or lower method used.

This method works in the similar manner to the first method. Difference is that, it is already defined in the library, so, the user does not need to write the same code each time he/she wants to convert the string.

Algorithm :

Input the string, using the getline() method.
We run a for loop, take each character of given string one by one.
Next, we pass the character in toupper() or tolower() and store it in the same place of the string.
Output the converted string.

Code:

#include <iostream>\n#include<string>\n\nusing namespace std;\n\nint main() {\n\tstring str;\n    cout<<\"Enter the string \";\n    getline(cin,str);\n\n\tfor(int i=0;i<str.length();i++)\n\t\tstr[i]=toupper(str[i]);\n\t\n    cout<<\"\\n The string in upper case:\"<<str<<\"\\n\";\n\t\t\n\tfor(int j=0;j<str.length();j++)\n\t\tstr[j]=tolower(str[j]);\n\t\n    cout<<\"The string in lower case: \"<<str<<\"\\n\";\n}\n

Output:

Enter the string: studymite\nThe string in upper case:STUDYMITE\nThe string in lower case: studymite\n

Extra Segment: Upper to lower, and lower to upper(toggle case):

Logic:

We use the logic of method 1, here.

Algorithm:

Input string
Check if it is a capital letter
If yes, convert it to small
If no(it is a small letter), convert it to capital.

Code:

#include <iostream>\nusing namespace std;\n\nint main()\n{\n\tstring str;\n    cout<<\"Enter the string \";\n    getline(cin,str);\n\tfor(int i=0;str[i]!='\\0';i++)\n\t{\n\t\tif (str[i]>=65 && str[i]<=90 )          //checking for uppercase characters\n\t\t\tstr[i] = str[i] + 32;          //converting uppercase to lowercase\n\t\telse if (str[i]>=97 && str[i]<=122 )\n\t\t    str[i] = str[i] - 32;              //converting lowercase to uppercase  \n\t}\n\t\n\t/*\n\tYOU CAN ALSO USE THIS METHOD  :-)\n\tfor(int i=0;str[i]!='\\0';i++)\n\t{\n    \tif (str[i]>=65 && str[i]<=90 )                  //checking for uppercase characters\n\t\t\tstr[i] = toupper(str[i]);       //converting uppercase to lowercase\n\t\telse if (str[i]>=97 && str[i]<=122 )    //checking for lowercase characters\n\t\t\tstr[i] = tolower(str[j]);       //converting lowercase to uppercase  \n\t}*/\n\tcout<<\"\\n The converted string: \"<< str;\n    return 0;\n}\n

Output:

Enter the string: ThIs Is ToGgLe CaSe\nThe converted string: tHiS iS tOgGlE cAsE\n

\n","title":"Program to Convert string to lowercase or uppercase in C++","authorDetails":{"name":"Juhi Kamdar","slug":"juhi-kamdar"},"description":"Learn to write a Program to convert strings to uppercase or convert strings to lowercase in C++ using Changing ASCII code method, inbuilt functions: toupper and tolower, toggleCase in C++.","slug":"cpp/examples/changing-case-in-strings-using-cpp/","articleId":"636a83457bb1ce5072622c15","bookmarkStatus":{"isBookmarked":false,"bookmarkId":null}}