Introduction to C

Introduction to C#

Relevant Reading

This lecture will cover contents from Chapter 1 - Appendix version of the book.

1. What is C?#

Overview#

Developed by Dennis Ritchie at Bell Labs
First public released in 1972.
The book: *The C programming languange” by Dennis M. Ritchie and Brian W. Kernighan. Prentice Hall 1988.

Scary stuff ahead …#

C is much less supportive for programmers than Java.
(Much) easier to make mistake, and (much) harder to fix.

But it is exciting …#

C requires less memory resources than Java.
C, in many instances, runs faster than Java.
Knowing C will make you a better programmer overall.

2. C and Java#

hello.c

#include <math.h>
#include <stdio.h>

/* main function definition: */
int main() {
    printf("Hello World\n");
    printf("sqrt(4) is %f\n", sqrt(4));
    return 0;  // main returns value 0
}

hello.java

import java.lang.Math;

/* define a HelloWorld class */
class Hello {

  /* main method definition: */
  public static void main(String[] args){
    System.out.println("Hello World");
    System.out.println("sqrt(4) is " + Math.sqrt(4));
  }
}

Similarities#

Values, types, literals, expressions
Variables
Control flow (if, switch, while, for, do-while)
Call-return: parameters, arguments, return values
Arrays (mostly)
Primitive and reference types
Type casting.
Library usage.

Differences#

C has no classes or objects (but something similar)
C is not object-oriented.
C arrays are simpler:
- No boundary checking.
- No knowledge of array’s own size.
String operations are limited.
No collections, exceptions, or generics.
No automatic memory management.
Pointers!!!

Running Java

Running C

3. Hands-on: Getting started#

SSH to molly. Refer to the Setup page if you need a refresher on how to do so.
Change into csc231 from inside your home directory.
- Your home directory is represented by the ~ sign.
Create a directory named intro-c inside csc231, then change into that directory.

cd ~/csc231
pwd
mkdir intro-c
ls
cd intro-c
pwd

Create hello.c#

Inside the terminal, make sure that you are still inside intro-c, then use nano to create hello.cwith the source code below.

pwd
nano -l hello.c

Once finished editing in nano:
- first hit Ctrl-X (same for both Windows and Mac).
- Next hit Y to save modified buffer (new contents).
- Hit Enter to save to the same file name as what you opened with.
Memorize your key-combos!.

What’s in the code?#

Line 1: Standard C library for I/O, similar to Java’s import.
Line 2-4: Function declaration/definition for main:
- Line 2:
  - return type: int
  - function name: main
  - parameter list:
    - argc: number of command line arguments.
    - *argv[]: pointers to array of command line argument strings.
- Line 3: Invoke builtin function printf to print out string Hello world! with an end-of-line character \n. This is similar to System.out.printf.
- Line 4: Exit a successfully executed program with a return value of 0.

Hands-on: Simple compile and run#

Similar to javac, we use gcc to compile C code.
Before compile, make sure that you are still inside intro-c in the terminal.

ls
pwd
gcc -o hello hello.c
ls
./hello

Hands-on: Compile and show everything#

There are a number of steps from C codes to executable binaries.

ls -l
gcc -save-temps -o hello2 hello.c
ls -l
./hello2

compile and run hello.c, keeping intermediate files

What are those?#

hello.i: generated by pre-processor
hello.s: generated by compiler.
hello.o: generated by assembler.
hello (or hello2): executable, generated by linker.

Hands-on: View files#

For hello.i and hello.s, they can be view on the editor.
Run the following command to view hello.i

cat -n hello.i

Run the following command to view hello.s

cat -n hello.s

For hello.o and hello, we need to dump the binary contents first.

xxd -b hello.o hello.o.txt
xxd -b hello hello.txt
ls -l

Run the following command to view hello.o.txt

cat -n hello.o.txt

Run the following command to view hello.txt

cat -n hello.txt

4. Challenge: output#

The usage of C’s printf is similar to Java’s System.out.printf. Find out how to modify hello.c so that the program prints out Hello Golden Rams! with each word on a single line. The program should use exactly one printf statement.

5. Input: scanf#

C formatting placeholders: (similar to Java)

%g: placeholder for a float (or double) value
%d: placeholder for a decimal value (int, short, char)
%s: placeholder for a string value
%c: placeholder for a char value

readInput.c

#include <stdio.h>

int main() {
  int num1, num2;
  printf("Enter a number: ");
  scanf("%d", &num1);
  printf("Enter another: ");
  scanf("%d", &num2);
  printf("%d + %d = %d\n", num1, num2, (num1+num2) );
  return 0;
}

InputReader.java

import java.util.Scanner;

class InputReader {
  public static void main(String[] args) {
    int num1, num2;
    Scanner in = new Scanner(System.in);
    System.out.print("Enter a number: ");
    num1 = in.nextInt();
    System.out.print("Enter another: ");
    num2 = in.nextInt();
    System.out.printf( "%d + %d = %d\n",
          num1, num2, (num1+num2) );
  }
}

6. Challenge#

Create a file called mixedInput.c that is modified from readInput.c. The file should do the followings:

Ask user to provide three input of type float
Print out the multiplication statement with all the multiplicants and results as done in readInput.c.

7. Conditionals and Loops#

Similar to Java.

Conditionals: compare.c

#include <stdio.h>

int main(void) {
    int num1, num2;

    printf("Enter the 1st number: ");
    scanf("%d", &num1);
    printf("Enter the 2nd number: ");
    scanf("%d", &num2);

    if (num1 > num2) {
        printf("%d is biggest\n", num1);
    } else if (num1 == num2) {
        printf("%d and %d are the same\n", num1, num2);
    } else {
        printf("%d is biggest\n", num2);
    }

    return 0;
}

Loops

forLoop.c

#include <stdio.h>

int main(void) {
    int num, i;

    printf("Enter a value: ");
    scanf("%d", &num);
    // make sure num is not negative
    if (num < 0) {
        num = -num;
    }

    for (i = 0; i < num; i++) {
        printf("%d\n", i);
    }

    return 0;
}

whileLoop.c

#include <stdio.h>

int main(void) {
    int num, val;

    printf("Enter a value: ");
    scanf("%d", &num);
    // make sure num is not negative
    if (num < 0) {
        num = -num;
    }
    val = 1;
    while (val < num) {
        printf("%d\n", val);
        val = val * 2;
    }

    return 0;
}

8. Function in C#

Almost the same as methods in Java, except for one small difference.
They need to either be declared, or must be defined prior to being called (relative to written code position).

9. Arrays#

Statically declared arrays
Multiple data values of the same types
Adjancent locations in memory (we will talk about this in the future)
Inside the terminal, make suse that you are still inside intro-c, then use nano to create array-1.cwith the source code below.

What is the distance between addresses? Why?
Compile and run array-1.c