C language----functions

First, the definition:

A collection of code fragments with specific functionality, we become functions.

Second, return value:

1. The return value of the function is called the value of the function and can only be returned to the keynote function through the return statement;
2, a function can have only one return value;
3, the function even if there is no return value can also use return to end the execution of the function, return to the keynote function;
4. The statement after return is no longer executed.

Third, formal parameters, actual parameters

1. Formal parameters
Appears in the definition of the function, with a false name to represent the value to be provided when the function is called.
2.
An expression that appears in a function call.

Note: When a function is called, the contents of the formal participant copy argument are a way to convey information to the function.

Iv. function declarations

Strict functions usually consist of three parts: function declaration, function definition, and function tuning.

V. Recursive invocation of functions

1,//For the function of recursive call must do a good analysis, the derivation of the recursive expression, n * Multiplefun (n-1), and in order to prevent the loop call itself causes the program into a dead loop, we must find the conditions of the end of the call, such as factorial is the condition of 1 o'clock stop loop call

2, the so-called recursive call function to implement the internal loop call itself until the condition is not satisfied.

Six, example code:

Enter a month and date to calculate the day ordinal of the year?#import <Foundation/Foundation.h>intSumvalue (intn);intDayOfYear (intYearintMonthintDay);intMainintARGC, const char * argv[]) {//    intn =0;//    printf("Please enter a number:");//scanf"%d", &n);//    printf("1 ~ %d and is %d\ n", N, Sumvalue (n));//    printf("Please enter date and year information:");intYear =0, month =0, day =0; scanf"%d/%d/%d", &year, &month, &day);printf(%d%d months  %d is  the day of the year.  \ n ", year, month, Day, DayOfYear (year, month, day));return 0;}intSumvalue (intN) {intSum for(inti =1; I <= N; i++) sum + = i;returnsum;}intDayOfYear (intYearintMonthintDay) {intDays[] = { to, -, to, -, to, -, to, to, -, to, -, to};//If the entered month is greater than A, or the date is greater than toIndicates an input error, directly ends the input, and returns0Daysif(Month > A|| Day > to)    {return 0; }if(Year% -==0|| (Year%4==0&& Year% -!=0)) {days[1] = in;//If it is a leap year, the2The value of the month is changed to inOr no action is done, the default -Days}//define an shaping variable to save the date first, and then pass forLoop consecutively plus the number of days of all full months before the current given month, and finally return the resultintDaysofyear = day; for(inti =0; I < month-1;    i++) {daysofyear + = Days[i]; }returnDaysofyear;}

C language----functions