What are functions in C language? What is the difference between functions in programming and functions in mathematics? Understanding functions in programming languages

        When many kids just learned programming , I don't know the difference between functions and methods .java Medium call method ,C Language is also called function ,javascript Also called function ... confused and disoriented .

        Actually , They come from two words :function( function ) And method( Method ). The effect is basically the same , however , My personal understanding is ： Methods are more class dependent , Exists in object / Classes are called methods , The function is not . And then gradually it was not a special distinction .

         Just learning programming Language When , Some little friends don't know the function in the programming language . today , I will explain the role of functions in programming languages from the perspective of mathematical functions !

Well known , Functions in mathematics are generally like this :

 y =  2 * x

It is estimated that this formula can be understood after having studied the most basic primary function estimation in Grade 8 or above .

that , When he was in x When taking different values ,y It can also change accordingly .

        If you write this formula in your code , It looks like a general 2*x The result of is assigned to y ,y What you receive is 2*x Of expression Return value !

        Pay attention to the word : Return value . In the future you will hear the word again and again .

        At this point, if you write a separate calculation when x yes 2、3、8、10 Value ,

        In Mathematics , Insert the above values one by one x Operation in , Get the corresponding y

        The same is true in programming languages ,

        however , Suppose you want to do some more complicated operations in the same way ( Here is the output sentence : Plug in xxx Carry out operations )

        ( For the convenience of demonstration , Open and write )：

#include <stdio.h>
int main(){
    int x,y;

    x = 2;
    printf(" Plug in 2 Carry out operations \n");
    y = 2*x;
    printf("%d\n",y);

    x = 3;
    printf(" Plug in 3 Carry out operations \n");
    y = 2*x;
    printf("%d\n",y);

    x = 8;
    printf(" Plug in 8 Carry out operations \n");
    y = 2*x;
    printf("%d\n",y);

    x = 10;
    printf(" Plug in 10 Carry out operations \n");
    y = 2*x;
    printf("%d\n",y);

    return 0;
}

          Because the operation is too simple , But if it's a very complicated equation , This makes the code redundant . Then we can use the concept of function .

        The first C Let's talk about the format of language functions !

        [ return type ]   [ Function name ] ([ Function parameter ]...){

                // The operation performed with the passed parameters

        }

        The return value type can be the basic data type ( Such as int,char,float,double...), The returned data is the data of the processing function ！

        that , The formula can be encapsulated into a function ( Suppose the function name is a):

int a(int x){
    printf(" Substituted %d Calculate !\n",x);
    return 2 * x;
}

         This is the most basic one C Format of language function , In the middle of the parentheses is the parameter . What values do you want to process , Just pass in the value （ You can also choose not to transmit anything , But parentheses cannot be omitted ）, The type passed in must be the same as the type defining the parameter , The type of the received return value must be the same as the return value type !( For example, the return value of this example is int type , Also used for receiving int type )

        here , The original code can be written as , You can also complete the same operation as just now ：

# include <stdio.h>

int main(){
    int x,y;

    x = 2;
    y = a(x);
    printf("%d\n",y);

    x = 3;
    y = a(x);
    printf("%d\n",y);

    x = 8;
    y = a(x);
    printf("%d\n",y);

    x = 10;
    y = a(x);
    printf("%d\n",y);

    return 0;
}

          Some students will feel , This also returns a value , And then output . Since functions can be reused , Why not pack it all in ? You can do the same , But at this time, we should pay attention to ： When a function does not need to return anything to the caller , The return value type can be written as void 了 , But this time , You can no longer take any variables to receive the return value of this function .

        The complete code is as follows :

#include <stdio.h>
void a(int x){
    //  Declare a variable to save x The result of the treatment 
    int y;
    printf(" Substituted %d Calculate !\n",x);
    y = 2 * x;
    printf("%d\n",y);
}
int main(){
    int x;

    //  When calling a function, the function will output 
    //  So there is no need to write one by one printf    

    x = 2;
    a(x);


    x = 3;
    a(x);

    x = 8;
    a(x);

    x = 10;
    a(x);

    return 0;
}

         here , Programming “ function ” The concept and mathematics of “ function ” The concept of . But it is obvious that functions in programming are much more flexible than those in mathematics ！