1. Problem Solving using Computers

COMP 1100 – Computer Programming 1
Lecture 1:
Problem Solving using Computers
• Architecture of a Computer
• Illustration of a Problem
Science starts only with problems
- Karl Popper
• How a Computer Solves a Problem
• Algorithms
Problem Statement
Input/Output Description
Algorithm Development
Summer 2011
Prepared by: Roger Gajraj
Architecture of Computer
Control Processing Unit (CPU)
Control Unit
Arithmethic &
Logic Unit (ALU)
System Bus
Architecture of Computer
Input unit
– Takes inputs from the external world via a variety of input devices keyboard, mouse,
temperature sensors, odometers, wireless devices etc.
Output Unit
– Sends information (after retrieving, processing) to output devices –monitors/displays,
projectors, audio devices, switches, relays, gearbox etc.
System Bus
– Place where information is stored.Control
– Used by the other units to communicate with each other.
ALU – Arithmetic and Logic Unit
– Processes data; add, subtract, decision – after Arithmethic
comparing with data,
& for example
Logic Unit (ALU)
– Controls the interaction among other units.
– Knows each unit by its name, responds to requests fairly, reacts quickly on certain critical
events. Gives up control periodically in the interest of the system.
– Together with the ALU is called the CPU.
System Bus
Architecture of Computer
– Can fetch an instruction from memory
– Execute the instruction
Control Unit
– Store the result in memory
Arithmethic &
• AInput
program – a
set of instructions
Logic Unit (ALU)
• An instruction has the following structure:
– Operation operands,
Architecture of Computer
• Input can be taken from real world and
processed to produce useful output.
• A computer program can be created by a
programmer to instruct the computer how to
process data.
Problem Solving
• The student must read the problem statement a
number of times to ensure that he/she understands
what is asked before attempting to solve the problem.
• The following steps need to be followed:
1. read the problem carefully
2. understand what the problem entails
3. and only then, write down the steps to solve the
• An everyday example will be:
– I need to go to school. Write down the steps to take from
waking up in the morning until I am at school.
Problem Solving
1. Wake up.
2. Get out of bed.
3. Wash.
4. Put on clothes.
5. Prepare something to eat.
6. Eat.
7. Take my bag.
8. Go to school.
• your steps must always be in a logical order!
• These steps are called an algorithm that can be defined
as a set of sequential instructions to solve a problem.
• The most important aspect of solving a problem by
using a computer is to write an algorithm to solve it. An
algorithm is a set of steps that must be written in such
a way that is it unambiguous and precise. The
computer cannot think for itself – you as the
programmer must tell the computer exactly what to
do. You may never assume that the computer will do
something if you have not explicitly included the
specific step.
• Think of an algorithm as a recipe.
• We can re-use this recipe to
– take specific ingredients(input)
– cook them together(processing)
– produce some food(output)
• An algorithm to solve a computer based problem consists of 3
phases i.e.
What you have available for the algorithm to solve the problem
How you are going to solve the problem i.e. what steps you are
going to take
What is the required result
• An algorithm must receive data (input) that must be
processed to render meaningful results (output or
• In other words:
• Input is processed to render meaningful output.
• Data is processed to render meaningful information.
Expressing algorithms
• Sequence of worded steps
• Pseudocode
• Flowcharts
• Calculate the sum of 2 numbers and display the result on the
– Input: Not available in the problem statement. The user has to supply
– numbers.
– Processing: Add the 2 numbers to determine the sum.
– Output: The sum as calculated in the processing phase is displayed on
the screen of the computer.
• Note the following:
– The value of the numbers must be available before the sum can be
– calculated.
– It is impossible to display the sum before it has been calculated.

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