Control Structures Nguyen Dung

Falculty of Information Technology

Hue University of Science

Content

Selection

if statement

switch statement

Iteration (loop)

for statement

while statement

do … while statement

Jump:

break

continue

return

goto 2

if statement

Syntax 1st:

if ( expression ) {B;}

exp

B

nonzero

zero

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if statement

Example:

int a = 5, b = 9, max;

max = a;

if ( max < b ){

max = b;}

printf(“Max is: %d”,max);

Max is: 9

if (max < b)

max = b;

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if statement

Syntax 2nd:

if ( exp ) {B1;}

else {B2;}

exp

B1

nonzero zero

B2

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if statement float a, b, x;

printf(“a = ");scanf("%f",&a);

printf(“b = ");scanf("%f",&b);

if (a == 0 ){

if ( b != 0 )

printf(“Equation hasn’t root.”);

else

printf(“Equation has countless root.”);

}

else{

x = -b/a;

printf(“Root of equation is x = %f”,x);

}

a = 2

b = 6

Root of equation is x = -3.00

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Excercises

1. Xác định xem một số nguyên là chẵn hay lẻ.

2. Xác định học lực dựa vào điểm trung bình của sinh viên, biết:

3. Xác định số có giá trị lớn hơn trong hai số thực a, b theo 2 cách: sử dụng lệnh if và không sử dụng lệnh if

4. Hiển thị một số tự nhiên bất kì từ 0 đến 9 dưới dạng chữ.

ĐTB [0, 4) [4, 5) [5, 6.5) [6.5, 8) [8, 9) [9, 10]

Học lực Kém Yếu Trung bình Khá Giỏi Xuất sắc

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exp==

exp1

exp==

exp2

…

exp==

expn

B0;

B1;

B2;

Bn;

Zero

Zero

Zero

Zero

Non-Zero

Non-Zero

Non-Zero

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switch statement

Syntax:

switch (exp)

{

case (exp1):

B1; break;

case (exp2):

B2; break;

...

case (expN):

BN; break;

[default: B0;]

}

expression

Constant-expression

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Example:

void main()

{ int x;

printf("Nhap so: ");

scanf("%d", &x);

switch(x){

case 0: printf(“Khong”);break;

case 1: printf(“Mot”);break;

case 2: printf(“Hai”);break;

case 3: printf(“Ba”);break;

case 4: printf(“Bon”);break;

case 5: printf(“Nam”);break;

case 6: printf(“Sau”);break;

case 7: printf(“Bay”);break;

case 8: printf(“Tam”);break;

case 9: printf(“Chin”);break;

}

getch();

}

Nhap so: 6

Sau

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while .. do statement

Syntax:

while (exp)

{

B;

} exp B;

Zero Non-Zero

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Example

Find “greatest common divisor” of a and b.

Then find “least common multiple” of a and

b

Input: a, b

Output: GCD(a,b) and LCM(a,b)

Method:

𝐺𝐶𝐷 𝑎, 𝑏 =

𝑎 𝑖𝑓 𝑏 = 𝑎

𝐺𝐶𝐷 𝑎 − 𝑏, 𝑏 𝑖𝑓 𝑎 > 𝑏

𝐺𝐶𝐷 𝑎, 𝑏 − 𝑎 𝑖𝑓 𝑎 < 𝑏

𝐺𝐶𝐷 𝑎, 𝑏 =𝑎𝑏

𝐿𝐶𝑀 (𝑎, 𝑏)

𝐺𝐶𝐷 𝑎, 𝑏 = 𝑎 𝑖𝑓 𝑏 = 0

𝐺𝐶𝐷 𝑏, 𝑏 𝑚𝑜𝑑 𝑎 𝑖𝑓𝑏 ≠ 0

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Implement unsigned int x, y, a, b;

printf("Nhap x, y: ");

scanf("%d,%d", &x, &y);

if (x == 0 && y == 0)

printf(“Both a and b are 0\n");

else if (x * y == 0){

printf(“GCD(%d,%d) is: %d\n", x, y, x+y);

}

else{

a = x;b = y;

while(a != b){

if (a > b)

a -= b;

else

b -= a;

}

printf(“GCD(%d,%d): %d\n", x, y, a);

printf(“LCM(%d,%d) is: %d\n",x, y,(x*y)/a);

}

unsigned int r = 0;

while(b!=0){

r = a % b;

a = b;

b = r;

}

13

do .. while statement

Syntax:

do

{

B;

}

while (exp);

exp

B;

Zero

Non-Zero

Different with

while statement??? 14

Example

#include <stdio.h>

#include <conio.h>

void main()

{

int x; char c;

do{

printf(“\nEnter x: ”);

scanf(“%f”, &x);

if (x%2==0){

printf(“%d is even”,x);

}

else

printf(“%d is odd”,x);

printf(“\nPress ESC to exit... ”);

c = getch();

} while (c!=27);

}

Enter x: 6

6 is even

Press ESC to exit...

Enter x: 7

7 is odd

Press ESC to exit...

15

for statement

Syntax:

for(exp0;exp1;exp2)

{

B;

} exp1

exp0;

Zero

Non-Zero

B;

exp2; 16

Example

Find the following sum:

S = 1 + 2 + 3 + ... + n = 𝒊𝒏𝒊=𝟏

Input: n

Output: sum of n number from 1 to n

Method:

s = 0;

For i = 1 to n do

s = s + i;

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Implement

#include <stdio.h>

#include <conio.h>

void main()

{

int n, s=0;

printf(“Enter n: ");

scanf("%d", &n);

for(int i = 1; i <= n; i++)

s = s + i;

printf(“Sum is: ", s);

getch();

}

Enter n: 6

Sum is: 21

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break, continue, goto

The break command allows you to terminate

and exit a loop (that is, do, for,

and while) or switch command from any point

Example

int s = 0;

for(int i = 0; i <= 10; i++){

if (i == 5)

break;

s = s + i;

}

printf(“s = %d”,s);

s= ???

19

break, continue, goto

The continue statement jumps the next

loop.

Example

int s = 0;

for(int i = 0; i <= 10; i++){

if (i == 5)

continue;

s = s + i;

}

printf(“s = %d”,s);

S = ???

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break, continue, goto

Goto: self-study

21

return

The return statement:

terminates the execution of a

function

or return a result(address or value)

to the calling function and exit

function.

Syntax:

return exp;

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Warning Homework

Please visit website

to get it.

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Questions

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The end

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