How to Print an Integer Using the putchar() function

This is a C program that defines a function named print_number() which takes an integer value as a parameter and prints it to the console. It also has a main() function which calls the print_number() function with the integer value 1028 as an argument.

Let's take a closer look at the code:

#include <stdio.h>

This line includes the standard input/output header file which contains functions for input and output operations.

void print_number(int num)

This line defines a function named print_number() which takes an integer value num as a parameter and does not return a value (i.e., it has a void return type).

unsigned int number;

This line declares an unsigned integer variable named number.

if (num < 0)
{
    number = -num;
    putchar('-');
}
else
{
    number = num;
}

This code block checks if the value of num is negative. If num is negative, it takes the absolute value of num and stores it in number, and then it prints a minus sign to the console. If num is not negative, it simply assigns the value of num to number.

if (number / 10)
{
    print_number(number / 10);
}
putchar('0' + (number % 10));

This code is a recursive function that prints out the digits of a positive integer number in reverse order. Here's how it works:

The function takes in an integer number as its argument.
The condition if (number / 10) is the same as if (n / 10 != 0). In other words, the body of the if statement will execute as long as n / 10 is not zero
Inside the curly braces, the function calls itself recursively with print_number(number / 10). This means that the function is called again with number divided by 10. This will continue until number becomes less than 0 or 0, at which point the condition will evaluate to false, and the recursive calls will stop.
After the recursive calls have stopped, the function executes putchar('0' + (number % 10)). This prints out the last digit of the original number by taking the remainder of number divided by 10, and adding it to the ASCII code of the character '0'. This converts the digit to its corresponding ASCII code and prints it out as a character.
Because the recursive calls were made in reverse order, the digits are printed out in reverse order as well.

For example, if we call the function with number equal to 123, the following steps will occur:

if (123 / 10) evaluates to true, the function calls itself with print_number(12).
if (12 / 10) evaluates to true, the function calls itself with print_number(1).
if (1 / 10) evaluates to false, the function does not call itself again.
putchar('0' + (1 % 10)) prints out the character '1'.
The function returns to the previous call with number equal to 12.
putchar('0' + (12 % 10)) prints out the character '2'.
The function returns to the initial call with number equal to 123.
putchar('0' + (123 % 10)) prints out the character '3'.
The function exits.

Thus, the output of calling print_number(123) would be "321".

int main(void)
{
    int num = 1028;
    print_number(num);
    putchar('\n');
    return (0);
}

This is the main function of the program. It declares an integer variable named num and assigns it the value 1028. It then calls the print_number() function with num as the argument to print the value of num to the console. Finally, it prints a newline character to the console using putchar('\n') and returns 0 to indicate successful program completion.