C tolower() function

C tolower(int c)

The tolower() function is used to translate uppercase characters to lowercase characters. The function is defined in the ctype.h header file.


int tolower(int argument);

tolower() Parameters:

Name Description Required /Optional
ch Argument ch represents a uppercase letter. Required

Return value from tolower()

  • Upon successful completion, tolower() returns the lowercase letter corresponding to the argument passed; otherwise returns the argument unchanged.

Example: How tolower() function works?

#include <stdio.h>
#include <ctype.h>

int main() {
    char ch;
     printf("Convert upper case to lower case:\n");
    ch = 'W';
    printf("%c -> %c", ch, tolower(ch));

    ch = 'x';
    printf("\n%c -> %c", ch, tolower(ch));
    ch = 'Y';
    printf("\n%c -> %c", ch, tolower(ch));
    ch = 'A';
    printf("\n%c -> %c", ch, tolower(ch));
    return 0;


Convert upper case to lower case:
W -> w
x -> x
Y -> y
A -> a

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What's an object file in C?

An object file is the real output from the compilation phase. It's mostly machine code, but has info that allows a linker to see what symbols are in it as well as symbols it requires in order to work. (For reference, "symbols" are basically names of global objects, functions, etc.)

A linker takes all these object files and combines them to form one executable (assuming that it can, i.e.: that there aren't any duplicate or undefined symbols). A lot of compilers will do this for you (read: they run the linker on their own) if you don't tell them to "just compile" using command-line options. (-c is a common "just compile; don't link" option.)

Ref : https://bit.ly/3CbzF8M