What are the knowledge points of C language functions?

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A preliminary study of the functions in the program

The concept of function

A function is a program part with a specific function (can be used as a black box)

Function has a clear way to use (fixed input corresponds to fixed output)

A function is reusable in a program (a tool in a program).

Type of function

Data processing (data → data)

Process x into y by some rule, such as: y = 2x + 1

Process definition (data → function)

Perform a series of actions (based on data) to perform a function, such as screen printing

The components of functions in C language

Function name: unique identification of the function

Function parameter definition: data input (data → data, data → action)

Function return type:

Data output (data → data)

No return value (data → action)

Examples of generalized functions:

Returns the type function name (parameter 1, parameter 2)

{

Program statement 1

Program statement 2

.

Program statement n

}

Examples of functions in C language

Function call

Call a defined function through the function name

When a function is called, you need to specify the specific values of the function parameters in turn.

The result (return value) of a function call can be saved in a variable of the same type.

Let's take a look at the code for a function call:

# include int func_demo (int x) {int y = 0; y = 2 * x-1; return y;} int main () {int R1 = func_demo (1); int R2 = func_demo (5); int R3 = func_demo (10); printf ("R1 =% d\ n", R1); printf ("R2 =% d\ n", R2); printf ("R3 =% d\ n", R3); return 0;}

The following is the output:

Let's take a look at another piece of code that writes a function to calculate the sum:

# include int sum (int n) {int r = 0; int I = 0; for (iTun1; I