What does %d mean in the C programming language?

In the C programming language, %d is a format specifier that is used in printf() and scanf() functions to indicate that an integer argument should be formatted or read.

When using printf(), %d is used to format an integer value and print it to the standard output. For example, the following code will print the value of the variable x to the console:

code
int x = 42;
printf("The value of x is %d\n", x);

The output of this code will be:

code
The value of x is 42

When using scanf(), %d is used to read an integer value from standard input. For example, the following code will read an integer value from the console and store it in the variable x:

code
int x;
printf("Enter an integer value: ");
scanf("%d",&x); 
This code will print the message "Enter an integer value: " to the console, wait for the user to enter a value, and then store the entered value in the variable x.

In both cases, %d is used to indicate that an integer value should be formatted or read, and the corresponding argument is passed as a separate argument to the function using the printf() or scanf() function.