This chapter discusses functions in C programming. It covers binary/standard functions that come with C libraries and are declared in header files. User-defined functions can be created by the programmer. The format for declaring a function includes its return type, name, parameters, and code block. Functions can be void, with a return value, or take arguments. Variables used in a function have either local or global scope.

1. Chapter 4
Function
Mr.Warawut Khangkhan
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2. Contents
Binary function or Standard function.
User defined function.
Format function declaration.
Type of functions.
The score of variables.
Mr.Warawut Khangkhan Chapter 4 Function 2

3. FUNCTION
Mr.Warawut Khangkhan Chapter 4 Function 3

4. Function
F F F
main( ) F F F
F C F F2
F (Library Function) F F
F F F F F (User
Defined Function)
Mr.Warawut Khangkhan Chapter 4 Function 4

5. BINARY FUNCTION OR
STANDARD FUNCTION
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6. Binary function or Standard
function
F F F C
F F F F F F
,F F F
F
F
Mr.Warawut Khangkhan Chapter 4 Function 6

7. Binary function or Standard
function (Cont.)
F C F F .h
F header file F F
F header file F F
F F F math.h
F F F F string.h
Mr.Warawut Khangkhan Chapter 4 Function 7

8. Binary function or Standard
function (Cont.)
F F F
#include <header file> F F
F C F F
F F F header file F
F F F F
F F F
Mr.Warawut Khangkhan Chapter 4 Function 8

9. Example lib_func.c
#include <stdio.h>
#include <math.h>
int main( ) {
int x, y;
printf(“Enter number: “);
scanf(“%d”, &x);
y = sqrt(x);
printf(“Square root of %d = %d”, x, y);
system(“PAUSE”);
return 0;
}
Mr.Warawut Khangkhan Chapter 4 Function 9

10. USER DEFINED
FUNCTION
Mr.Warawut Khangkhan Chapter 4 Function 10

11. F F
(User defined function)
F C F F
F F
F F F C F F F
F F
F F F F
F F F F F F
F F F
Mr.Warawut Khangkhan Chapter 4 Function 11

12. User defined function (Cont.)
(Cont.)
F F F F
F FF F
F F
F F
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13. FORMAT FUNCTION
DECLARATION
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14. F C
(Format function declaration)
type function-name ( type arg-1, type arg-2, … ) {
local variable declaration;
statement-1;
statement-2;
statement-3;
…
statement-n;
return ( value );
}
Mr.Warawut Khangkhan Chapter 4 Function 14

15. Example ex_func.c
#include <stdio.h> void main( ) {
line( );
void line( ) {
int i; printf(“Welcome to
for (i=0; i<30; i++) C Programmingn”);
printf(“*”); line( );
printf(“n”); }
}
Mr.Warawut Khangkhan Chapter 4 Function 15

16. TYPE OF FUNCTIONS
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17. F
(Type of functions)
F F F3
F F / F F
F F F F
F F F F
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18. F F / F F
F F F F F F
F F (Argument) F F F
F F F F F F
F F FF F F F F
F
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19. F F
F F F F F
F F (Argument) F F F
F F F F F F F
F F F F F3 int, float
int F F F F F F
F F F F F
F int, float int
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20. F F F F
F F F F
F F F F F F F
F F F F
F F F F F F
F F F
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21. F F F F
(Cont.)
variable = function-name ( arg-1, arg-2,
… );
F F F F F F return
F F F
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22. THE SCORE OF
VARIABLES
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23. (The score of variables)
C F F F
F 2
◦ global
◦ local
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24. global
global F F external
F F F
F global F
F F F F F F
F F F F F F
F
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25. global (Cont.)
F global
F F
global F F
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26. local
local F F
automatic F F
F local F F
F F F F F
F F F F F
local F F F
F F F
F F F local F
F
Mr.Warawut Khangkhan Chapter 4 Function 26