Extra Notes

1. Comments

• Comments are notes ignored by the compiler, used to explain code.

• Single-line: // like this

• Multi-line: /* for longer notes */

On-Board Activity

Write a C code snippet that prints your name but includes at least one comment explaining what the code does.

(Ask: What happens if you remove the comment markers?)

2. Constants and Variables

• Constant: Value cannot change after definition, e.g. #define PI 3.14

• Variable: Value can change, must be declared with a data type first, e.g. int age = 16;

On-Board Activity

Declare a constant for your school’s year and a variable for the number of students. Print both values using printf().

3. Data Types

• Common types: int (integer), float (decimal), char (character)

• Example: float price = 99.50;

On-Board Activity

Declare three variables (integer, float, character). Assign them values and display all three with an appropriate output function.

4. Format Specifiers

• Used with printf() and scanf()

  • %d for int, %f for float, %c for char, %s for strings

On-Board Activity

Given the variable declarations int a = 5; float b = 3.2; char c = 'A';, write a printf statement to display all three values on different lines.

5. Output Functions

• putchar(c): prints a single character

• puts(str): prints a string with a new line

• printf(): prints formatted output

On-Board Activity

a) Use putchar() to print the first letter of your name.

b) Use puts() to print a greeting.

6. Input Functions

• scanf(): gets formatted input

• getchar(): gets one character

• getch(), getche(): get characters (difference—getche() echoes, getch() does not)

• gets(): gets string input (but not recommended for new code)

On-Board Activity

Write code to input a character using getchar(), and a number using scanf(), then print both values.

7. Assignment and Compound Assignment Operators

• = assigns a value: x = 5;

• Compound: x += 3; (means x = x + 3;), similar for -=, *=, /=

On-Board Activity

If x starts at 5, write code that increases x by 10 using a compound assignment. Show the value before and after.

1. Comments

Code Example

c
// This code prints my name
printf("Ali\n");

Removing "//" makes it regular code, not a comment.

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2. Constants and Variables

Code Example

c
#define SCHOOL_YEAR 2025        // constant
int students = 40;             // variable
printf("Year: %d\n", SCHOOL_YEAR);
printf("Number of students: %d\n", students);

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3. Data Types

Code Example

c
int rollNo = 12;
float percentage = 87.5;
char grade = 'A';

printf("Roll: %d\n", rollNo);
printf("Percentage: %f\n", percentage);
printf("Grade: %c\n", grade);

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4. Format Specifiers

Code Example

c
int a = 5;
float b = 3.2;
char c = 'A';

printf("%d\n", a);
printf("%f\n", b);
printf("%c\n", c);

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5. Output Functions

Code Example

c
putchar('A');             // prints: A

puts("Hello Class 10!");  // prints: Hello Class 10!
                          // and adds a new line

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6. Input Functions

Code Example

c
char ch;
int num;

ch = getchar();                   // input one character
scanf("%d", &num);                // input one integer

printf("Character: %c\n", ch);
printf("Number: %d\n", num);

(Note: For getch() / getche() and gets(), you generally need to include conio.h for older compilers. Modern C discourages gets() and recommends fgets().)

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7. Assignment and Compound Assignment Operators

Code Example

c
int x = 5;
printf("Before: %d\n", x);

x += 10;       // same as x = x + 10;
printf("After: %d\n", x);

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You can ask any student to come up and write any of these on the board. If you want full explanations or variations, just ask!