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THE CS NOTES

Int in C++

int n;

if n in global scope n=0 otherwise undetermined

int a, b; ✅

int a=b=0 ❌

Compile Error ❌

int func; // Variable declaration
void func() {} // Function declaration

you cannot declare a function and a variable with the same name in the same scope, but you could declare them in different scope. This is because it would create ambiguity for the compiler

Convert char to its ASCII value:

char ch = 'C';
int a = int(ch); ✅// Explicit conversion, ASCII value of 'C' is 67
int b = ch; //✅ Implicit conversion, also results in 67

Convert char to its numerical value (‘1’ to 1):

char ch = '5';
int a = ch - '0';  // '5' - '0' = 5-0;
// Ascii Value of 5 - Ascii Value of 0 = 5

Read a whole line (even if include whitespace)

#include iostream
std::string str;
std::getline(std::cin, str);
int a=1;


if(a) cout<<1, a++; ✅
if(a) cout<<1, return 1; ❌

Note: comma operator allows two or more expressions to be executed sequentially, but return is a control statement, not an expression, so it cannot be used in this way.

bool with Arithmetic Operations in C++

bool a = true, b = false, c = 3, d = 0;
int e = 1;
int sum = a + b + c + d + e; // 1 + 0 + 1 + 0 + 1 = 3
  • bool behaves like integers (0 or 1) in arithmetic.
  • Any non-zero assigned to bool becomes true (i.e., 1).
  • In expressions, bool values are added like int.

Cpp Invalid Variable Declaration

int a, b, c = 0, 1, 2; // ❌ Only 'c' initialized to 2, rest are undeclared
int a = 0, int b = 1, int c = 2; // ❌ Wrong syntax

Cpp valid Variable Declaration

int a = 0, b = 1, c = 2; // ✅ Preferred: single-line declaration
int a = 0; int b = 1; int c = 2; // ✅ Valid but less clean
  • In C++, type is specified once per declaration line.
  • int a, b = 0, 1; means only b is initialized with 1; a is uninitialized.
  • Unlike Python/JS, C++ doesn’t support unpacking style (a, b, c = 0, 1, 2).