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Srivaths P
C++ Basics
(Part 1)

Why you should prefer C++
(For Competitive Programming)
• Efficiency and Speed
• Most popular language for CP
• In-built Data Structures and Algorithms (STL)

Goal
To understand:
• Constants and datatypes in C++
• Input/Output in C++
• Various C++ operators
• Conditional statements
• Loops
Be able to write simple programs at the end, such as a
prime number checker.

Simplest C++ program
#include <iostream>
using namespace std;
int main() {
cout << "Hello world!" << endl;
}

Constants in C++
• Integer constants: 4 | 62 | -90
• Decimal constants: 3.14 | 12.0 | 0.33333
• Character constants: 'f' | '5' | '~' | 'n'
• String literal: “Hello :D” | “MyP@ssw0rd123!”

Output in C++
To output a value, we use the cout operator as
follows: cout << value;
To print multiple values in the same line:
cout << value1 << value2 << value3;
To start printing in a new line: endl or ‘n’

Arithmetic operators in C++
Arithmetic Operators:
1) + Addition
2) - Subtraction
3) * Multiplication
4) / Division (Quotient)
5) % Modulo (Remainder)
NOTE: C++ follows the BODMAS rule

Variables
Variables are containers that stores specific types
of data. They can be modified with the
assignment operator “=”
Syntax: datatype variable_name = value;

Variables
Variable names cannot:
• Have spaces (use underscore instead)
• Start with a digit
• Be reserved by the compiler
• Already taken by another variable (in the same scope)
NOTE: Keywords/Variables are case sensitive

Datatypes
Datatypes are used to set the “type” of a
variable. For example, int is used to declare
integer variables.
Two types of datatypes:
• Primitive datatypes
• Derived datatypes

Common Primitive datatypes
1. int (long long int, unsigned int, etc.)
2. char
3. bool
4. float (double, long double)
5. Special type: void

Common Derived datatypes
1. string
2. vector
3. map
4. set
5. priority_queue

Arithmetic Assignment Operators
1. +=
2. -=
3. *=
4. /=
5. %=

Unary Operators
Operators that only need one value/operand
are called unary operators.
1. +
2. -
3. ++
4. --

Input in C++
To output a value, we use the cin operator as
follows: cin >> value;
To print multiple values in the same line:
cin >> value1 >> value2 >> value3;
NOTE: Each value must be separated by a space
or a new line when taking input.

Check your understanding - 1
1. How will you declare a character equal to
exclamatory mark?
2. Take an integer input, and output the value
multiplied by 7.
3. Take two values a, b as input, and output three
values: a+b and a*b and a/b
a/b should be a decimal, not an integer

Conditions and
Relational Operators
Conditions return a boolean value depending on whether
the expression is true or false.
Conditional operators:
==, !=
Relational operators:
<, >, <=, >=

Logical operators
Logical operators perform operations on boolean values or
expressions that result in Boolean values.
1. “(expr1) && (expr2)” checks whether BOTH are true.
2. “(expr1) || (expr2)” checks whether EITHER one is true.
3. “!(expr)” returns the OPPOSITE of the result of “expr”
The operators are called AND, OR, NOT operators respectively

Conditional statements
Conditional statements execute a different block of code
depending on the boolean value of a condition.
Syntax: if (condition) {
// something
} else if (another_condition) {
// something
} else {
// something
}

Check Your Understanding 2
1. Take input of 3 numbers x, y, z and output the maximum
using if statements
2. Given marks of a student, grade them from A to D
1. Between 0 and 30 -> D
2. Between 30 and 65 -> C
3. Between 65 and 90 -> B
4. Between 90 and 100 -> A
5. Output “Error” if less than 0 or greater than 100.

Loop
Loops are used to repeat a block of code until some
condition is satisfied.
There are three types of loops in C++:
1. for loop
2. while loop
3. do-while loop

Loop (Miscellaneous)
• An iteration is defined as one time the loop gets
executed. For example, 3rd iteration is the 3rd time the
loop is run.
• “break” statement exits the current/innermost loop
when executed.
• “continue” statement skips to the next iteration of the
current/innermost loop when executed.

“for” loop
Syntax:
statement1: Executed once before start of loop.
statement2: Condition of the loop. Loop exits if false.
statement3: Executed after each iteration.
for (statement1; statement2; statement3) {
// Code here
}

“while” loop
Syntax:
Check if the condition is true and then execute
the block of code. Repeat.
while (condition) {
// Code here
}

“do-while” loop
Syntax:
Execute the block of code and then check if
the condition is true. Repeat.
do {
// Code here
} while (condition);

Scope
A scope is a region of the program.
Every pair of curly braces creates a new
scope.
The variables inside the scope cannot be
used outside the scope.

Miscellaneous
• A loop inside another loop is called nested loops.
Syntax:
• Infinite loops are loops that run forever and never end
(when the condition is always true)
for (s1; s2; s3) {
for (s4; s5; s6) {
// Code here
}
}

goto statements
Goto/Jump statements are used to skip to another part of the
code.
Considered as bad practice to use goto statements except if it
used to exit from a nested loop.
Syntax:
label: // creates the label to skip to
goto label; // skips to the specific label

Check Your Understanding 3
1. Find the sum of the first N natural numbers (Using loops)
2. For the first N natural numbers:
If number is divisible by 3 and 5, print FizzBuzz
If number is divisible by 3, print Fizz
If number is divisible by 5, print Buzz
3. Print a N x M grid similar to the following:
1 2 3 4
5 6 7 8
9 10 11 12

Exercise
Write a program to take a number N as an input, and
output whether it is a prime number or not.
(Do not worry about efficiency)

Resources
• https://www.programiz.com/cpp-programming (learning C++ in general)
• https://www.programiz.com/cpp-programming#flow-control (if-else and loops)
• https://www.programiz.com/cpp-programming/nested-loops (nested loops)
• https://www.programiz.com/cpp-programming/goto (goto statements)

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C_BASICS FOR C PROGRAMMER WITH SRIVATHS P

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