L-3: SSH, Autolab, Variables, Types, scanf #

Sandeep Nagar

Part-1

SSH, Autolab(pingala), pingala shell, Autograder

Part-2

Comments, Identifiers, Variables, Types, Constants, scanf, Controle Flow
L-3 Slides: https://cpro-iiit.github.io/docs/course_material/lectures/3/lec_3.pdf Reference code: https://tinyurl.com/yuhchnuj Programiz, web editor: https://tinyurl.com/bdd55vwn

What is SSH, and how do I use it? #

ssh sandeep.nagar@pingala.iiit.ac.in

• Connects to pingala server (at IIIT with Linux OS with all programs required for the course installed).
• Why?: All students will work in the same environment (os same, programs same, etc.)

Log in over SSH #

ssh user_name@pingala.iiit.ac.in
Enter your CAS password

• You can work on the remote machine using your local computer.

• You can edit, create, and copy files on the server.

• Submit assessments using your local machine to Autolab.

Autolab: #

For automatic evaluation and grading of programs.

Two ways to submit for auto-grading:

• pingala shell: using ssh shell (prefered)

• GUI: user interface, using pingala.iiit.ac.in website

Questions about Autolab/ssh/pingala?

Running the Program on shell #

1. Run gcc compiler to get the executable file main gcc main.c -o main
2. Run the executable main ./main

Comments for C: #

• Whole-line comment
• Partial line comment
• Multiple line comment

•       // This is a whole-line comment
        variable = 5; // this is partial line comment
        /* and 
        comment
        comment
        ..
        */          
  

  Programiz, web editor: https://tinyurl.com/bdd55vwn

Identifiers: #

• Unique names that are assigned to variables, structs, functions, and other entities.
• Allow us to name data and other objects in the program.
• Each identifier object in the computer is stored at a unique address.

Rules to create identifiers:

• First character must be alphabetical or underscore ‘_’
• Must contain only alphabetical characters, digits, or underscore
• The first 63 characters of an identifier are sufficient
• Can not duplicate a keyword

E.g. for identifiers #

a               // valid
my_name         // valid
_your_name_     // valid 
_Bool           // valid 
_bool           // valid but not same as _Bool 
Student Name    // invalid
int             // not valid, int is a keyword
char            // not valid, char is a keyword 
2_name          // invalid, starting with digit
I_am-Yoda       // invalid, '-' not allowed

Constants: #

Constants are data values that can not be changed during the execution of a program. Like variables, constants have a type.

Constant types:

• Boolean, character, integer, real, complex, and string constants.

Variables: #

Void, Character, Integer

Variable Initialization: #

Character Types: #

// char, 1 byte (= 8 bit)

printf("%c", _char_)

Integer Types: #

short, int, long, long long

• Size of integers

    size of (short) ≤ size of (int) ≤ size of (long) ≤ size of (long long)
  
    2 byte -> 4 byte = 4 byte -> 8 byte
  

Floating-point type: #

• float, double, long double

    size of (float) ≤ size of (double) ≤ size of (long double) 
    4 byte -> 8 byte -> 16 byte
  

Type summary: #

Type summary: #

Symbolic names for control characters #

• Some common control characters along with their symbolic names:

  1.  Newline:           `\n`       printf("\n")
  2.  Horizontal tab:    `\t`       printf("\t")
  3.  Vertical tab:      `\v`       printf("\v")
  4.  Backspace:         `\b`       printf("\b")
  5.  Carriage return:   `\r`       printf("\r")
  6.  Form feed:         `\f`       printf("\f")
  7.  Alert (bell):      `\a`       printf("\a")
  8.  Backslash:         `\\`       printf("\\")
  9.  Single quote:      `\'`       printf("\'")
  10. Double quote:      `\"`       printf("\"")
  11. Question mark:     `\?`       printf("\?")
  12. Null character:    `\0`       printf("\0")
  

scanf() #

• Function reads data from the standard input stream stdin into the given locations.
• Reads format-string from left to right

int a = 5; scanf("%d", &a);

scanf() #

scanf() #

scanf() #

Control Flow #

• Condition is an expression (or series of expressions) e.g. n < 3 or x < y || z < y

• Operators Precedence and Associativity: some operations are done before others when evaluating an expression.

  Parentheses: ()                                 // first
  Postfix operators: ++, --
  Unary operators: +, -, !, ~, ++, --, (type)
  Multiplicative operators: *, /, %
  Additive operators: +, -
  Relational operators: <, >, <=, >=
  Equality operators: ==, !=
  Logical AND operator: &&
  Logical OR operator: ||
  Assignment operators: =, +=, -= ... and so on   // last 
  

Associativity: #

When expressions contain operators of the same precedence level, their evaluation order is determined.

• Left-Associative: operators are evaluated from left to right, +, +

  • e.g.a + b - c will first evaluate a + b and then subtract c from the result.

• Right-Associative: are evaluated from right to left, e.g. =

  • e.g. a = b = c, c is assigned to b, and then the resulting value of b is assigned to a.

Crucial for correctly interpreting and writing C programming expressions.

Questions? #

Reading #

Next: Conditional Statements: if, else, while, switch, break, continue.

• Chapter 3: Computer Science: A Structured Programming Approach Using C Behrouz A. Forouzan, Richard F. Gilberg

• More about scanf : https://www.ibm.com/docs/en/i/7.4?topic=functions-scanf-read-data

• Programiz, web editor: https://tinyurl.com/bdd55vwn

• http://courses.washington.edu/mengr477/resources/Precedence.pdf