常见伪代码指令及使用

1. 声明statement

1.1 Assignment statement赋值语句

variable = expression

e.g将表达式3 * 4赋给变量result:

result = 3 * 4

1.2 compound statements 复合语句

begin

statement1

statement2

end

1.3 conditional statements条件语句

1）

if condition then

statement

e.g

if a < 0 then

a = -a

abs = a

output abs

2）

if condition then

statement

else

statement

e.g

if a > 0 then

abs = a

else

abs = -a

output abs

2. Iterative statement迭代语句

2.1 For loop

for var = start_value to end_value do

statement

1. Var首先被赋值start_value。

2. 如果var<=end_value，执行语句。

3.Var加1然后回到步骤2.

e.g1计算前n个数的和

input n

sum = 0

for i = 1 to n do

begin

sum = sum + i

end

output sum

该循环被执行了n次

2.2 While loop

while condition do

statement

*此处condition指‘继续的条件'

1. 如果condition为真，则执行语句

2.否则停止

3.回到步骤1

e.g1计算前n个数的和

input n

sum = 0

i = 1

while i <= n do

begin

sum = sum + i

i = i + 1

end

output sum

e.g2 计算所有(键盘)输入数字的总和:

sum = 0

while (user wants to continue) do

begin

ask for a number

sum = sum + number

end

output sum

2.3 repeat-until

repeat

statement

until condition

*此处condition为结束的条件

1. 执行语句

2. 如果condition为真,停止

3. 回到步骤1

e.g1 计算所有(键盘)输入数字的总和:

sum = 0

repeat

ask for a number

sum = sum + number

until (user wants to stop)

output sum

来点练习，一题三解：

e.g 求区间[x, y]内所有整数的乘积，假设x和y都是整数

for：

product = 1

for i = x to y do

begin

product = product * i

end

output product

while：

product = 1

i = x

while i <= y do

begin

product = product * i

i = i+1

end

output product

repeat：

product = 1

if x <= y then begin

i = x

repeat

product = product * i

i = i+1

until i > y

output product

end

e.g 列出给定正整数x的所有因数

for：

for i = 1 to x do

begin

if (x%i == 0) then

output i

end

while：

i = 1

while i <= x do

begin

if x%i == 0 then

output i

i = i+1

end

repeat：

i = 1

repeat

if x%i == 0 then

output i

i = i+1

until i > x