C Programming - Variables and I/O Lecture 2

Variables and I/O

• Today's Topics: Variables, input/output formats, arithmetic computations.

Output - printf

• printf: Used to display text and data on the screen.
• printf is a family of functions, including fprint, vsprintf, sprintf, to print to files and variables.
• Arguments: Specify what to print inside parentheses.
• Format Specifiers: Use placeholders like %d (integers) and %f (floating-point numbers) within strings to display values from variables. Example string: "The value is %d", %d is replaced with an integer variable.
• Multiple Output: Can print multiple variables in one printf statement

printf Special Characters

• \n: Newline
• \r: Carriage return
• \b: Backspace
  • \n: important when flushing the buffer, crucial for debugging

Type Conversion and Arithmetic Operations

• Combine different data types in expressions, result will be a double
• Multiplying by 1.0 converts to a double, effectively changing the operation's type.
• Converting data types may cause rounding. c = a + b, then d = c - a, d may not equal b due to rounding.

Input - scanf

• scanf: A function from the standard library to read input from the keyboard.
• Syntax: It follows a similar format to printf using specifiers.
• Pointers: Crucial: Input functions like scanf require pointers & to reference variables.

Operators

• Standard mathematical operators +, -, *, / are used.
• Follow the usual mathematical order of operations..
• Note that integer division results in an integer value.

Initialization

• Reading a variable before assigning a value might lead to unexpected results or errors (especially in larger programs).
• Some compilers issue warnings for this potential problem (using flags, for example -W with GCC).

math.h

• math.h: A mathematical library providing standard functions.
• Includes: Header file #include <math.h>
• Constants: Predefined values like pi, e
• Functions: Functions like log, sqrt, sin and so on.
• Compilation: Needs a special compilation flag (-lm, for example) for the compiler to include math.h correctly.

Conclusion

• printf and scanf are necessary to communicate with the screen and keyboard.
• Variable declaration must be done before use.
• While spaces and tabs are not required by the compiler, they improve code readability.