printf() and scanf() in C The printf() and scanf() functions are used for input and output in C language. Both functions are inbuilt library functions, defined in stdio.h (header file). printf() function The printf() function is used for output. It prints the given statement to the console. The syntax of printf() function is given below: 1. printf( "format string" ,argument_list); The format string can be %d (integer), %c (character), %s (string), %f (float) etc.