Bài giảng Tin học đại cương A (dành cho khối tự nhiên): Control Structures

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

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if statement
Syntax 1st:
if ( expression ) {B;}

zero

exp
nonzero

B

3


if statement
Example:
int a = 5, b = 9, max;
if (max < b)
max = b;
max = a;
if ( max < b ){
max = b;}
printf(“Max is: %d”,max);

Max is: 9

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if statement
Syntax 2nd:
if ( exp ) {B1;}
else {B2;}
zero

nonzero

exp

B2

B1

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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:
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

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.

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exp==
exp1

B1;

Non-Zero
Zero
exp==
exp2

B2;

Non-Zero

Zero

…
Zero
exp==
expn

Bn;

Non-Zero
Zero
B0;

8


switch statement
Syntax:

expression

switch (exp)
{
case (exp1):
B1; break;
case (exp2):
B2; break;
...
case (expN):
BN; break;
[default: B0;]

}

Constant-expression

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Example:
void main()

{

Nhap so: 6
Sau

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();

}

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while .. do statement
Syntax:

while (exp)
{
B;
}
exp

B;

Non-Zero
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:

𝑎 𝑖𝑓 𝑏 = 𝑎
𝐺𝐶𝐷 𝑎, 𝑏 = 𝐺𝐶𝐷 𝑎 − 𝑏, 𝑏 𝑖𝑓 𝑎 > 𝑏
𝐺𝐶𝐷 𝑎, 𝑏 − 𝑎 𝑖𝑓 𝑎 < 𝑏

𝑎 𝑖𝑓 𝑏 = 0
𝐺𝐶𝐷 𝑎, 𝑏 =
𝐺𝐶𝐷 𝑏, 𝑏 𝑚𝑜𝑑 𝑎 𝑖𝑓𝑏 ≠ 0
𝑎𝑏
𝐺𝐶𝐷 𝑎, 𝑏 =
𝐿𝐶𝑀 (𝑎, 𝑏)

12


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{
unsigned int r = 0;
a = x;b = y;
while(b!=0){
while(a != b){
r = a % b;
if (a > b)

a = b;
a -= b;
b = r;
else
}
b -= a;
}
printf(“GCD(%d,%d): %d\n", x, y, a);
printf(“LCM(%d,%d) is: %d\n",x, y,(x*y)/a);
}

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do .. while statement
Syntax:

do
{

B;

B;
}
while (exp);

Non-Zero
exp

Zero

Different with
while statement???

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Example

Enter x: 6
6 is even
Press ESC to exit...
Enter x: 7
7 is odd
Press ESC to exit...

#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);
}

15


for statement
Syntax:
for(exp0;exp1;exp2)
{
B;
}

exp0;

Zero
exp1

Non-Zero
B;

exp2;

16


Example
Find the following sum:
S = 1 + 2 + 3 + ... + n =

𝒏
𝒊=𝟏 𝒊

Input: n
Output: sum of n number from 1 to n
Method:

s = 0;
For i = 1 to n do
s = s + i;
17


Implement
#include <stdio.h> Enter n: 6
#include <conio.h> Sum is: 21
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();
}

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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;
s= ???
}
printf(“s = %d”,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;
S = ???
}
printf(“s = %d”,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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