Iterative statements in C++ and Python (Part 2)

for loop iterative statements

Executing set of statements using for iterative statement in C++ and Python is quite different.

First, lets look how C++ implement iterative method using the for method. In C++, for loop is better suites for situations where number of iterations are known.

Syntax

for (initialization : condition : modifier )
{
      statement 1;
      statement 2;
            ...
}

The initialization, condition, and modifier do not need to be placed inside the brackets.

Example

for (int a=0 ; a<=10 ; a++)
{
      cout<<a<<" x2 = "<<a*2<<endl;
}

or

int a = 0;
for ( ; a<=10 ; )
{
      cout<<a<<" x2 = "<<a*2<<endl; 
      a++;

}

In Python, for loop can be used in various ways as shown in the following examples

Syntax

for variable in sequence:
      statement 1
      statement 2
            ...

example 1

for num in range (1,10)
      print num

This will print number 1,2,3,4,5,6,7,8,9
The range function use the following syntax : range (start, end, step).
 
for num in range (2,10,2)
      print num

output
2
4
6
8


example 2

for letter in 'Monday':
    print 'letter value : ', letter

output
letter value : M
letter value : o
letter value : n
letter value : d
letter value : a
letter value : y


example 3

weekdays = ['Monday','Tuesday','Wednesday','Thursday','Friday']
for name in weekdays:
    print 'weekday - ',name

output
weekday - Monday
weekday - Tuesday
weekday - Wednesday
weekday - Thursday
weekday - Friday

example 4
for m in range(2,15):
    a = 0
    for n in range (1, m/2+1):
        if m%n == 0:
            a = a+1
    if a==1:
        print 'prime number - ',m

output
prime number -  2
prime number -  3
prime number -  5
prime number -  7
prime number -  11
prime number -  13

Iterative statements in C++ and Python (Part 1)

while iterative statement

Set of statements can be executed repeatedly until a condition is met.

C++	Python
Syntax while (condition) {         statement1;         statement2;                 ... }	Syntax while condition:         statement1;         statement2;                 ...
Example int num = 1;  while (num<=10) {       cout<<num<<"x2="<<num*2;       num = num+1; }	Example num = 1 while num<=10:      print("%d x2 = %d"%(num,num*2))      num = num + 1

Conditional statements in C++ and Python (part 3)

if else if conditional statement

Multiple conditions can be checked using if else if (in C++) and if elif (Python). In the following example, two numbers are compared and three possible conditions are checked. The else is used to check the last or the default condition if all the other conditions have failed.

C++	Python
Syntax if (condition1) {         statement1;         statement2;                 ... } else if (condition2) {         statement1;         statement2;                 ... } else {         statement1;         statement2;                 ... }	Syntax if condition1:         statement1;         statement2;                 ...  elif condition2:         statement1;         statement2;                 ...  else:         statement1;         statement2;                 ...
Example int a = 10; int b = 15; if (a<b) {       cout<<"a < b."; } else if (a>b) {       cout<<"a > b."; } else {       cout<<"a = b."; }	Example a,b = 10, 15; if a<b:      print("a < b")  elif a>b:      print("a > b") else:      print("a = b")

Conditional statements in C++ and Python (part 2)

if else conditional statement

In the if else conditional statement, one set of statement(s) is executed if the condition is true, otherwise, the other set of statement(s) is executed.

C++	Python
Syntax if (condition) {         statement1;         statement2;                 ... } else {         statement1;         statement2;                 ... }	Syntax if condition:         statement1;         statement2;                 ...  else:         statement1;         statement2;                 ...
Example int a = 10; int b = 15; if (a<b) {       cout<<"a < b."; } else {       cout<<"a >= b."; }	Example a,b = 10, 15; if a<b:      print("a < b")  else:      print("a >= b")

Conditional Statements in C++ and Python (part 1)

if conditional statement

A condition is checked and execute statement/block of statements if the condition is true.

C++	Python
Syntax if (condition) {         statement1;         statement2;                 ... }	Syntax if condition:         statement1;         statement2;                 ...
Example int a = 10; int b = 15; if (a<b) {       cout<<"a < b."; }	Example a,b = 10, 15; if a<b:      print("a < b")

Indentation in C++ and Python

C++

---

Indentation has no effect on the program but make it more organize and reader friendly. The braces or curly brackets makes the statement blocks for the tasks.

if (10 < 20)
        cout<<"10 is less than 20";
else
        cout<<"10 not greater than 20";
        cout<<"This is second line";

Output
10 is less than 20
This is second line


Python

---

Indentation makes the statement blocks. No need to use the braces.

if 10 < 20:
        cout<<"10 is less than 20";
else:
        cout<<"10 not greater than 20";
        cout<<"This is second line";

Output
10 is less than 20

The output will be different if the indentation of the above python code is changed as follows.

if 10 < 20:
        cout<<"10 is less than 20";
else:
        cout<<"10 not greater than 20";
cout<<"This is second line";

Output
10 is less than 20
This is second line

Comments in C++ and Python

Comments are put in a program to make it more readable and easy to understand when someone reads it.

C++

---

There are two commenting styles

1. Line comment
Put two slashes (//) and whatever is been typed will become a comment and will be ignored by the compiler.

E.g.

int total = 0; // integer variable to store the total value


2. Block comment
This consist two parts: Starting with slash and star (/*) and ending with the reverse order , which is star and a slash (*/). Everything typed between these two symbols become comments and ignored by the compiler. Multiple comment lines can be made with the block comment method.

E.g.

/*-----------------------------
    Author : Randima
    Date   : 2017 January 01
-----------------------------*/


Python

---

A line starts with hash symbol (#) is a comment. Unlike block commenting in the C++, hash symbol (#) should be used in every comment line.

E.g.

#    Author : Randima
#    Date   : 2017 January 01