1. CSCI 161: Introduction to Programming
Lecture 3:
First Program
Data representation

2. First Program //library inclusion //function “main” //display string
#include <iostream>
using namespace std;
int main() {
cout << ”Hello world.”;
return 0; }
//library inclusion
//function “main”
//display string

3. Programming Errors Vocabulary and grammar - syntax
Rules determine if statement legally constructed - syntax rules
Compiler checks rules - gives syntax errors
Programs also contain errors in logic - bugs
Debugging - finding & fixing logic errors

4. A program to output the sum of two numbers

5. A more flexible program: read the two numbers from console
#include <iostream> using namespace std; int main() { int num1, num2; //two int variables to hold the two numbers int sum; //variable sum to hold the result of the sum of the two numbers //input the two numbers, first print message to the users on what they need to input cout << "please input two numbers:" << endl; cout << "num1 = "; cin >> num1; cout << "num2 = "; cin >> num2; //calculate the sum, store the result in variable sum sum = num1 + num2; //output the result cout << "the sum is " << sum << endl; return 0; }

6. Variable
A variable should be declare as with a type:
Examples:
int num1, num2; //two int variables to hold the two numbers int sum;
Type example
int, char, string

7. Running the program Wrong result! What happen? A run:
please input two numbers:
num1 = 2
num2 = 3
the sum is 5
Another run:
num1 = 450
num2 = 300
the sum is 750
One more time
please input two numbers:
num1 =
num2 =
the sum is
Wrong result!
What happen?

8. Data Representation

9. Components of a Computer
Start with components of a computer again to talk about memory and data representation.
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Memory
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Memory Cells
memory cell
an individual storage location in memory
address of a memory cell
the relative position of a memory cell in the computer’s main memory
contents of a memory cell
the information stored in a memory cell, either a program instruction or data
stored program concept
a computer’s ability to store program instructions in main memory for execution
…..
Memory cells contain a bunch of 0 and 1s.
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12. Figure 1.5 Relationship Between a Byte and a Bit
Byte
Bit
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Memory
data storage
setting the individual bits of a memory cell to 0 or 1, destroying its previous contents
data retrieval
copying the contents of a particular memory cell to another storage area
random access memory (RAM)
the part of main memory that temporarily stores programs, data, and results
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Memory
read-only memory (ROM)
the part of main memory that permanently stores programs or data
volatile memory
memory whose contents disappear when the computer is switched off
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Memory
secondary storage
units such as disks or flash drives that retain data even when the power to the drive is off
disk
thin platter of metal or plastic on which data are represented by magnetized spots arranged in tracks
optical drive
device that uses a laser to access or store data on a CD or DVD or Blu-ray Disk
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File System
file
named collection of data stored on a disk
directory
a list of the names of files stored on a disk
subdirectory
a list of the names of files that relate to a particular topic
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17. Internal Representation
Each unit of memory a two-state device
off or on, 0 or 1
represent in Binary, two Binary Digits (bits)
Organized into groups of 8 bits - bytes
represents single keyboard character
Larger grouping of 16 or 32 bits - word
represents single integer value
identified by address for access

18. Memory Sizes Kilobyte (K) = 210 = 1,024 bytes
Megabyte (Mb) = 220 = 1,048,576 bytes
Gigabyte (Gb) = 230 = 1,073,741,824 bytes

19. Decimal Number Systems
Base 10
Digits - 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
e.g =
= 3 x x x100
= 3 x x x 1 =

20. Binary Number System Base 2 Digits 0, 1 e.g. 1102 =
= 1 x x x 20
= 1 x x x 1 =
= 6

21. Counting in Binary Decimal Binary 0 0 1 1 2 10 3 11 4 100 5 101 6 110
Decimal Binary

22. How many symbols can N digit represent?
3 digit allows representing 8 numbers (symbols): 0-7
: – 15
N N