Constants and literals in C++ - Step-by-Step Execution

Concept Flow - Constants and literals

Start

↓

Define literal value

↓

Assign to constant variable

↓

Use constant in code

↓

Attempt to change constant?

Yes→Error: Cannot modify constant

No↓

Program runs using constant

↓

End

This flow shows how a literal value is assigned to a constant variable, which cannot be changed later in the program.

Execution Sample

C++

const int days_in_week = 7;
int main() {
  int total_days = days_in_week * 4;
  return total_days;
}

This code defines a constant for days in a week and calculates total days in 4 weeks.

Execution Table

Step	Action	Variable	Value	Note
1	Define constant days_in_week	days_in_week	7	Constant assigned literal 7
2	Enter main function	-	-	Program starts main
3	Calculate total_days	total_days	28	4 * days_in_week = 4 * 7 = 28
4	Return total_days	-	28	Program returns 28
5	Attempt to modify days_in_week	days_in_week	Error	Cannot modify constant - compile error

💡 Program ends after returning total_days; constant cannot be changed

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
days_in_week	undefined	7	7	7
total_days	undefined	undefined	28	28

Key Moments - 2 Insights

Why can't we change the value of days_in_week after defining it?

Because days_in_week is declared as a constant (const), the compiler prevents any modification after initialization, as shown in step 5 of the execution_table.

What is the difference between a literal and a constant?

A literal is a fixed value written directly in code (like 7), while a constant is a variable that holds a literal or value and cannot be changed, as seen in step 1 where 7 is assigned to days_in_week.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of total_days after step 3?

A 4

B 7

C 28

D Undefined

💡 Hint

Check the 'Value' column in row with Step 3 in execution_table.

At which step does the program try to modify the constant and cause an error?

A Step 5

B Step 2

C Step 3

D Step 4

💡 Hint

Look for the step mentioning 'Attempt to modify days_in_week' in execution_table.

If we change the literal 7 to 8 in the constant definition, what will total_days be after step 3?

A 28

B 32

C 7

D 8

💡 Hint

total_days = 4 * days_in_week; changing days_in_week to 8 means 4*8=32.

Concept Snapshot

Constants and literals in C++:
- Literal: fixed value like 7
- Constant: variable declared with 'const' that cannot change
- Syntax: const type name = value;
- Using constants prevents accidental changes
- Compiler error if you try to modify a constant

Full Transcript

This lesson shows how constants and literals work in C++. A literal is a fixed value like 7. A constant is a variable declared with 'const' that holds a literal or value and cannot be changed later. The example defines days_in_week as a constant with value 7. Then it calculates total_days as 4 times days_in_week. The program returns 28. If you try to change days_in_week later, the compiler gives an error. This protects important values from accidental changes.