That line prints the literal text "Child: " followed by the decimal value of x and a newline. Example output (if x == 5):

Child: 5

Notes and common pitfalls

Include and make sure x is initialized: using an uninitialized variable is undefined behavior.The %d specifier expects an int. If x is not an int (long, long long, unsigned, pid_t, etc.) use the correct specifier (%ld, %lld, %u, %jd with cast to intmax_t, or the PRI* macros from ) or cast appropriately to avoid undefined behavior.If this printf is used after fork(), be aware of stdio buffering: if stdout was not flushed before fork, you may get duplicated output from parent and child. Adding a '\n' often forces a line-buffer flush when stdout is a terminal.

Minimal correct example

include

int main(void) {
int x = 5;
printf("Child: %d\n", x);
return 0;
}

If you meant something specific (fork behavior, wrong output, format mismatch), tell me the surrounding code or error and I’ll help further.