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tolower() function in C/C++

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  • Difficulty Level : Easy
  • Last Updated : 22 Sep, 2022
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The tolower() function is defined in the ctype.h header file. If the character passed is an uppercase alphabet then the tolower() function converts an uppercase alphabet to a lowercase alphabet.

int tolower(int ch);

Basically tolower() returns an int value and in C language we can user %c to convert that int value to char value. But in c++ typecasting is required like this:

char c = (char) tolower(‘A’);

Parameter: This method takes a mandatory parameter ch which is the character to be converted to lowercase.
Return Value: This function returns the lowercase character corresponding to the ch.
Below programs illustrate the tolower() function in C:
Example 1:-
 

C++




// C++ program to demonstrate
// example of tolower() function.
 
#include <iostream>
using namespace std;
 
int main()
{
 
    char c = 'G';
 
    cout << c << " in lowercase is represented as = ";
 
    // tolower() returns an int value there for typecasting
    // with char is required
    cout << (char)tolower(c);
}

C




// C program to demonstrate
// example of tolower() function.
 
#include <ctype.h>
#include <stdio.h>
 
int main()
{
 
    // Character to be converted to lowercase
    char ch = 'G';
 
    // convert ch to lowercase using toLower()
    printf("%c in lowercase is represented as = %c", ch, tolower(ch));
 
    return 0;
}

Output

G in lowercase is represented as = g

Example 2:-
 

C++




// C++ program to convert a string to lowercase
// using tolower
#include <bits/stdc++.h>
using namespace std;
 
int main()
{
 
    // string to be converted to lowercase
    string s = "GEEKSFORGEEKS";
   
    for (auto& x : s) {
        x = tolower(x);
    }
   
    cout << s;
    return 0;
}
 
// code is contributed by triangleofcoding

C




// C program to demonstrate
// example of tolower() function.
 
#include <ctype.h>
#include <stdio.h>
 
int main()
{
    int j = 0;
    char str[] = "GEEKSFORGEEKS\n";
 
    // Character to be converted to lowercase
    char ch = 'G';
 
    // converting every character to lowercase
 
    while (str[j]) {
        str[j] = tolower(str[j]);
        j++;
    }
 
    // printing the string
    for (int i = 0; i < j; i++)
        printf("%c", str[i]);
    return 0;
}

Output: 

geeksforgeeks

 

Note:  

If the character passed in the tolower() is any of these three

1. lowercase character

2. special symbol

3. digit

tolower() will return the character as it is.

Example 3:

C++




// C++ program to demonstrate
// example of tolower() function.
#include <iostream>
using namespace std;
 
int main() {
 
    string s="Geeks@123";
   
      for(auto x:s){
       
          cout << (char)tolower(x);
    }
   
    return 0;
}
 
//contributed by triangleofcoding

C




// C program to demonstrate
// example of tolower() function.
#include <ctype.h>
#include <stdio.h>
 
int main()
{
    int j = 0;
    char str[] = "GeEks@123\n";
    char ch;
 
    while (str[j]) {
        ch = str[j];
        putchar(tolower(ch));
        j++;
    }
 
    return 0;
}
// code is contributed by codersaty

Output

geeks@123

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