printf

"printf" is a function in the C-standard library that outputs text to standard output. Standard output is typically the terminal or debug console, depending on the system the program is running on. The f stands for formatted, allowing the function to output not just fixed strings, but also text with variable data in it.

Hello world

The simplest of all C-programs is known as "Hello world" program. It outputs "Hello world", using printf.

#include <stdio.h>

int main(void) {
  printf("Hello world!\n");
  return 0;
}

Using parameters

Parameters need to be specified in the format string. A parameter definition starts with a % character. A simple example with one numerical parameter looks as below:

  printf("Total sum is: %d\n", Sum);

Parameter specification

Type field

The Type field can be any of:

Character	Description
%	Prints a literal % character (this type doesn't accept any flags, width, precision, length fields).
d, i	int as a signed decimal number. %d and %i are synonymous for output, but are different when used with scanf() for input (where using %i will interpret a number as hexadecimal if it's preceded by 0x, and octal if it's preceded by 0.)
u	Print decimal unsigned int.
f, F	double in normal (fixed-point) notation. f and F only differs in how the strings for an infinite number or NaN are printed (inf, infinity and nan for f; INF, INFINITY and NAN for F).
x, X	unsigned int as a hexadecimal number. x uses lower-case letters and X uses upper-case.
s	null-terminated string.
c	char (character).