Functions of C language

function : A collection of lines of code that is written to perform certain functions. Can be called by the same program or other program.

function is the basic constituent unit of C language.

The advantages of the function : The code is more concise, easy to maintain, can improve the reusability of code.

How to customize a function :

return value type Function Name ( parameter )

{

function Body ;

return value ;

}

Life case : make Ham

Ham type Make Ham (Live pigs )

{

Kill a pig;

hair removal ;

cleavers ;

added starch ;

added Melamine ;

.....

packaging ;

out Ham ;

}

Attention:

1. Return value type: Can have a return value, or it can have no return value (void)

2. function Name: a name for the functions , similar to the name of a person ( simply say that the function names, convenient later call )

3. Parameters : raw Materials

functions in C are divided into built-in functions and custom functions

common built-in functions :

Built-in functions	Header file	Use
Double sqrt (double x)	Math.h	Calculation x the square root
Double pow (double x, double y)		Calculation x of the y Second Power
Double ceil (Double x)		not less than x the smallest integer, and to Double form Display
Double floor (Double x)		no more than x the maximum integer, and to Double form Display
int toupper (int x)	Ctype.h	if x is a lowercase letter, the corresponding uppercase letter is returned
int tolower (int x)		if x is uppercase, the corresponding lowercase letter is returned
int rand (void)	Stdlib.h	generate a random number
void exit (int retval)		Terminating Programs

Example :

//calculate 1~10 square root and cubic        inti; DoubleSquare,power;  for(i=1; i<=Ten; i++) {Square=SQRT (i);//using the sqrt (x) function to calculate the x square rootPower=pow (I,3);//Use the POW (x, y) function to calculate the y-square of xprintf ("the square root of%d is%.2lf, the cubic is%.2lf\n", I,square,power);//. 2lf:double type is accurate to two digits after the decimal point}

Floor () and ceil () functions:

//Floor (x);---> The largest integer not greater than X, not roundedprintf"Floor (12.1) =%f\n", Floor (12.1));// Aprintf"Floor ( -12.1) =%f\n", Floor (-12.1));//-13//ceil (x);---> Smallest integer not less than x, not roundedprintf"ceil (12.1) =%f\n", Ceil (12.1));// -printf"ceil ( -12.1) =%f\n", Ceil (-12.1));//-12

Get random Number:

// set Random seed, Time (NULL): Gets the number of seconds of the current 00:00:00 1970-01-01  for (i=0;i<; i++) {//  printf ("%d\t", Rand ()); // rand (): pseudo-random number, generated random number 0~32767 // generate a random number between 0~99 printf ("%d\t", rand ()%);}

Functions of C language