Overview Structure of a C program

Preprocessor directives (前置處理 )

Functions (函數 )

Remarks -- /* …; …;… */ or //…. (註解 )

//========================// example to demo C structure// by ytlu Feb 25, 2005// ========================#include <stdio.h>#include <math.h>#include “ytlutable.h” double do_input(void); void do_output(double, double);

int main(){ double x, y, z; x = do_input(); y = MY_PI * x / 180.; z = cos(y) ; do _output(x, z); return(0);}

double do_input(){ double r; scanf(“%lf”,&r); return r;}

void do_output(double p, double q){ printf(“cos(%lf) = %lf\n”,p,q); return;}

ytlutable.h:

#ifndef ytlu_table_#define _ytlu_table_#define _ytlu_table_#define MY_Pi 3,1415926#define MY_HBAR 6.24e-34#define KB 1.38e-23#endif

Prepocessordirectives

main

function1

function2

User-prepared include files placed in same directory with the executable

Preprocessor Directives

• #include <headfile>

• #include “headfile”

• #define symbolic values or functions

• Declare global variables #include <stdio.h> // 包含庫存程式的定義檔 #define MATHPI 3.141592653589793 // 定義符號 #define CV(n, m) (n*ncol + m) // 定義符號函數 int ncol=3, nrow=4, ndim; // 宣告全域變數 (函數 )

Structure of a Function

• Function’s type and name //函數名稱和型態• Arguments passed in //傳遞的幅數• Function body: //函數本體

– Variables declare //宣告變數– Statements //工作指令– Return value // 結果回傳

Function vlen() compute length of a vector

double vlen(double x, double y, double z)// 函數名稱 vlen 型態 double, 傳入三幅數 x, y, z

{ double r2; // 宣告變數 r2

r2 = x * x + y * y + z * z; // 計算 r2

return(sqrt(r2)); // 結果回傳 // 也可寫為 return sqrt(r2);

}

Variable types

• int a1, a2, a3; // 整數• long int c1, c2, c3; // 長整數

• short int b1, b2, b3; // 短整數• unsigned int ..; // 正整數• unsigned long int …; // 4-byte 正整數

• float r1, r2, r3; // 4-bybe 浮點實數

• double d1, d2, d3; // 8-byte 浮點實數

• char acd, bch; // 單一字元

Constants (using suffix)

• For example: a=4; b=1.23;• “4” is treated as an int, 1.23 as a double

(the default types). // 預設 4 為整數 , 1.23 為 8-byte 浮點實數

• Other type: a=4U; // unsigned int 正整數

b =8L; // long int 4-byte 整數

c = 1.23F; // float 4-byte 浮點

d = 1.2345L; // long double (10-byte)

Casting: (type)variable

• Consider: int a=1, b=2;

float c;

c = a / b;

printf(“c = %f\n”,c);

• Result: c = 0.000000

• Why? (int)a/(int)c = (int)(0.5) = 0

• Correction: c = (float)a / (float)b;

Statements in a function(函數執行指令 )

• Variables declaration // 宣告變數• Arithmetic expression // 算數運算• Logic expression // 邏輯運算• Loops // 迴圈• Call other functions // 呼叫函數

-- Library functions or your own functions • Return value // 結果回傳

Arithmetic expression

• Binary operators // 二元運算 = + - * / % *= += -= /= a *= b; // 等同 a = a*b;

• Unary operators // 單元運算 n++; n--; -a

n++; // 等同 n = n + 1;

Logic if statement

Syntax:

if ( condition ) { ………; ………; }

else if (condition2) { ………; ..……; }

else if (condition3)

{……..; ………;}

else {…..; ……;}

Logic expressions (true=1 false=0)

• a == b ; a != b

• a > b ; a < b ; a <= b ; a >= b

• && (and) eg. (( a > b) && (c <= d))

• || (or) eg. (( a > b) || (c > d))

if ( x > 0.0) { y = x * x; }

else { y = 0.0; }

Repeating Loops

Syntax:

for (start; condition; step)

{ …….; …….; ……; }

sum = 0;

for (i = 0 ; i < 10 ; i++) sum = sum + i;

for (i = 100 ; i > 0 ; i--) { j = i + 1; sum = sum + 1.0/(i*j); }

for (i = 100; i > 0 ; i -= 2) sum = sum + 1.0/(i * ( i + 1)) ;

Libray functions and head files

Headfile gives definitions of libray functions

• stdio.h – defines scanf(), printf(), …

• math.h – defines sin(), cos(), sqrt(), … • stdlib.h – defines system(“..”), rand(), atof(..),..

-- 編輯軟體所提供的 include 檔用 <…>-- 自己所編寫的 include “…”檔用 , 必須放在執行檔所在的目錄下 , 否則要把目錄包含在內 .

-- headfile only define 函數用法 (編輯用 ), 函數本身在 LIBRARY 目錄下 以 .a (.o) 檔存在 (link 用 )

Print to monitor (stdout)

Syntax: printf(format string, variable list);Format: %c %d %e %f %s %u %lf %le

printf(“i = %d j = %5d k = %2d\n”, I, j, k); printf(“cos(%lf) = %20.15lf\n”, x, cos(x)); printf(“exp(%lf) = %.15le\n”, x, exp(x));

Specail character: \n – new line

Input from keyboard (stdin)

Syntax: scanf(format string, address list);

Format: %c %d %f %h %s %lf %ld

scanf(“%d %lf”, &n, &x);

scanf(“%*s %lf %lf %lf”, &x, &y, &z);

Arithmetic functions

#include <math.h>

sinx = sin(x); // x in unit of radians

cos(x) ; tan(x); acos(x); atan(x); asin(x)

sqrt(x); abs(n); fabs(x); fmod(x, y)

pow(x, y); exp(x); log(x); log10(x)

cosh(x); sinh(x); tanh(x)

Program 001

• Write a c-code to check the following equality:

)cos(3)( cos4)3cos( aaa 3

Frequently Appeared Errors

• Typos: miss type, spelling error, ij,..• Undeclared variables or functions.• Forget “;” at the end of a statement.• Unmatched delimiters: { }, “ “, ( ).• Unmatched arguments in calling a function.• Run-time error:

a. typo i j within a loop control.b. logic error.c. problem related to mixed-type

arithmetic.

Program 002

Taylor expansion:

input x and n, then calculate exp(x).

compare with that from math libray.

n

i

n

n

xx

0 !)exp(

Guild to pratice 2Main()2. Input double x3. Pass x to function myexp(x) return value of exp(x)4. Display the values of x and exp(x)

Double myexp(double x)1. Initial tolerance, nlimit2. Initila term = 1.0; sum = 1.0;3. Do loop ii = 1, to nlimit4. Term = term *x / ii;5. Sum = sum + term;6. If (fabs(term) < tolerance) break;7. Else repeat steps 4-6;8. Return sum

while(condition) { ; ;} do {..;..;} while(condition);

int j ; double sum=0.0; for (j=1; j<100; j++) sum += 1.0/(doube)j;

int j=1; double sum = 0.0; while (j<100) { sum += 1.0/(double)j ; j++; }

int j=1; double sum = 0.0; do { sum += .0/(double)j; j++; } while(j <= 100);

Practice 1 separate from the main() the part for computing exp(x)

Input x and n

Call expval(x, n)

Input a

Continue or not?

main() expval(x, n)

Pass x and n

Return series sum

Calculate exp(x,n)

Practice 2: using reverse orderin summing Taylor series

)))...)))1(1

1(2

1...(

(......3

1(2

1(1

1!0

n

x

n

x

n

x

xxx

i

xn

i

i

1. initial summ = 1.0

2. a loop from j = n to j = 1

3. for each j do: summ = 1.0 + summ * x / j

Pratice 3

設計程式作下列工作 :

1. 讀進一個 random seed, 用來random 產生一個 0 – MAXIMUM 之間的整數 .

2. 讓 user 猜 MAX_GUESS 數 , 並提示所猜的太大或太小 .

3.輸出猜中 , 或失敗訊息 .

Flow chart 流程圖

begin

輸入 seed

產生謎數 answer

猜答計數 ntry=0

輸入猜答 guess

guess==answer?

計數 ntry+1

ntry >= MAX_TRY? answer>guess

告之太小

告之太大 輸出猜中信息

輸出失敗信息

end

yes

no

yesno

yesno

Functions needed

void srand(unsigned int) : 變化 random number 的產生 (defined in stdlib.h)

int rand() : 產生一個 random number (defined in stdlib.h)

int scanf(“format”, addresses) : keyboard 輸入變數 (defined in stdio.h)

int printf(“format”, variables) : 寫到 monitor (define in stdio.h)

Keywords of C

unsigned int : 宣告 unsigned 整數

while (logic expression) { } : while 控制迴圈

if (logic expression) {…}

else if (logic expression) {…}

else if (login expression) {…}

% : 兩整數除法得其餘數 .