C++ Program to Convert Uppercase to Lowercase

In this article, you will learn and get code on uppercase character/string to lowercase conversion in C++. The program is created with and without using standard library (or string) function. Here are the list of programs:

Uppercase Character to Lowercase without using string function
Program to deal with an invalid input
Uppercase String to Lowercase without using string function
Uppercase character/string to lowercase using string function, strlwr()

Uppercase Character

An uppercase character is basically an alphabet character written in capital letter. For example, C. ASCII values of all 26 uppercase alphabet characters are 65-90. Where 65 is the ASCII value of A, 66 is the ASCII value of B, and so on upto, 90 is the ASCII value of Z

Lowercase Character

A lowercase character is basically an alphabet character written in small letter. For example, c. ASCII values of all 26 lowercase alphabet characters are 97-122. That is, a→97, b→98, c→99, and so on.

Uppercase and Lowercase String

If all the characters available in a string are in uppercase, then it is called as uppercase string. And if all the characters of a string are written in lowercase, then it is called as lowercase string.

Note - String is a combination of more than one character. For example, CODESCRACKER (an uppercase string) or codescracker (a lowercase string)

Uppercase to Lowercase Formula

Since ASCII value of A (capital letter) is 65 and ASCII value of a (small letter) is 97. The difference between them is 32. Therefore, on adding 32 to the ASCII value of capital letter say A, then we'll get the ASCII value of its equivalent letter in lowercase. That is,:

65 (ASCII value of A) + 32 = 97 (ASCII value of a)

C++ Uppercase Character to Lowercase

To convert a character from uppercase to lowercase in C++ programming, you have to ask from user to enter a character in uppercase and then convert it into its equivalent lowercase character. Finally print the equivalent character in lowercase on output.

#include<iostream>
using namespace std;
int main()
{
    char chUpper, chLower;
    int ascii;
    cout<<"Enter the Character (in Uppercase): ";
    cin>>chUpper;
    ascii = chUpper;
    ascii = ascii+32;
    chLower = ascii;
    cout<<"\nIts Lowercase: "<<chLower;
    cout<<endl;
    return 0;
}

This program was build and run under Code::Blocks IDE. Here is its sample run:

Now supply the character input in uppercase say C and press ENTER key to print its equivalent character in lowercase as shown in the output given below:

In above program, when user enters C as an uppercase character input, then it gets stored in chUpper variable. So the statement given below:

ascii = chUpper;

Initializes the ASCII value of C to ascii. So, ascii = 67. Now the statement:

ascii = ascii+32;

initializes 67+32 or 99 to ascii. So the new value of ascii is 99, which is the ASCII value of c (lowercase). So the statement:

chLower = ascii;

Since, chLower is of char (character) type variable, therefore the character corrensponds to 99 (ASCII value) gets initialized to chLower. So chLower=c. Now print the value of chLower as output.

How to deal with an Invalid Input ?

If user enters an invalid input like an alphabet character that is already in lowercase or any other character like numbers, or special character, then follow the program given below. Previous program does not work correctly in this case.

#include<iostream>
using namespace std;
int main()
{
    char chUpper, chLower;
    int ascii;
    cout<<"Enter the Character: ";
    cin>>chUpper;
    if(chUpper>='A' && chUpper<='Z')
    {
        ascii = chUpper;
        ascii = ascii+32;
        chLower = ascii;
        cout<<"\nIts Lowercase: "<<chLower;
    }
    else if(chUpper>='a' && chUpper<='z')
        cout<<"\nAlready in Lowercase";
    else
        cout<<"\nInvalid Input!";
    cout<<endl;
    return 0;
}

Here is its sample run with user input D

Below is another sample run with user input d (already in lowercase):

And here is the final sample with user input 4 (not an alphabet):

C++ Uppercase String to Lowercase

Now let's convert string from uppercase to lowercase. The following C++ program asks from user to enter a string say CODESCRACKER (in uppercase) to change and print it into lowercase:

#include<iostream>
#include<stdio.h>
using namespace std;
int main()
{
    char strUpper[50]="", strLower[50]="";
    int i=0, ascii, chk=0;
    cout<<"Enter the String: ";
    gets(strUpper);
    while(strUpper[i]!='\0')
    {
        if(strUpper[i]>='A' && strUpper[i]<='Z')
        {
            ascii = strUpper[i];
            ascii = ascii+32;
            strLower[i] = ascii;
            chk++;
        }
        else
            strLower[i] = strUpper[i];
        i++;
    }
    strLower[i]='\0';
    if(chk==0)
        cout<<"\nString is already in Lowercase";
    else
        cout<<"\nLowercase of String: "<<strLower;
    cout<<endl;
    return 0;
}

Here is its sample run with string input as This is CodesCracker:

C++ Uppercase to Lowercase using Function

The question is, write a program in C++ that converts uppercase character or string to lowercase using string function. The answer to this question is given below:

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
int main()
{
    char str[50];
    int len;
    cout<<"Enter the Character/String: ";
    gets(str);
    len = strlen(str);
    if(len==1)
        cout<<"\nLowercase of Given Character: "<<strlwr(str);
    else
        cout<<"\nLowercase of Given String: "<<strlwr(str);
    cout<<endl;
    return 0;
}

Here is its sample run with string input CODESCRACKER: