1. What's a Computer? Monitor Disk Main mouse Memory Keyboard Network
Central
Processing
Unit
Keyboard
mouse
Main
Memory
Network
CPU: (stupid) brain of the computer
can do very simple tasks VERY FAST
add, write in memory...
Goal: Perform elaborate tasks by putting
together many simple tasks
HOW ?
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2. Memory and Data All data used by a program (numbers, names…) is
stored in the memory of the computer.
Think of memory as a (huge) pile of boxes
(called words) 1 2 3 4 5
Each box has a number
gives the location
Each box always contains a value
a succession of 0’s and 1’s
(a number in base 2)
BUT
can be interpreted in many ways
by a program
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3. Memory and Data Location 4 contains 0.981 4 0.9811 2 3 4
0.981
109
‘c’
3.1415
Location 4 contains 0.981
Location 2 contains the
letter ‘c’
In a program do not use the location number
(=address) explicitly:
don’t want to say
“take the content of box 4”
would drive us crazy!
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4. Instead: Use a name to refer to the content of a given box
a variable
Rule of programming:
A variable MUST be declared to indicate the
type of the variable (is it a character (letter),
an integer, a floating point number…?)
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5. Declaring Variables Many different types: some examples A C language
declaration
int number_of_children;
for integer
must end with
semi-colon (;)
no space in the variable name
use underscores (_)
have meaningful names
(NOT int nc;)
An integer can be 1, -46, (NOT 1.5, -2.3)
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6. for a floating point, that is 96.2, -14.9, -7.02e-11...
double temperature;
for a floating point, that is 96.2, -14.9,
-7.02e-11...
char middle_initial;
for a character, that is an individual
keyboard character,
e.g. ‘b’, ‘A’, ‘0’, ‘+’ (NOT ‘blue’)
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7. Examples double 4 0.981 int 109 3 2 char ‘c’ int 1 3.1415 double1 2 3 4
0.981
109
‘c’
3.1415
double
int
char
int
double
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8. Rules for naming variables
Rules for C identifiers
_ use letters, numbers, underscore:
employee_SSN
_ can’t start with a number or underscore:
_bad, 1_not_good
_can’t be a reserved word of the C language:
if, while, double, int
_ case sensitive:
temperature  Temperature
_ length: practically as long as you want
(but…)
_ meaningful names: account_balance
(NOT x22yz)
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9. Storing values into variables
Declare a variable
gives a name to the content
of a memory location
We get a box. But how to put something in it?
Or better said: How to store the value of
a variable in the memory?
One way: Use an assignment statement
a declaration
int number_of_children;
number_of_children = 3;
an assignment
statement (don’t
forget ;)
A statement tells the CPU to do something.
A declaration is NOT a statement.
There are many kinds of statements.
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10. The structure of a C program
preprocessor
directive
#include <stdio.h>
int main(void) {
variables declarations
program statements
return 0; }
beginning of
program
end of
program
DON’T WORRY about what is in the boxes
Explanations will come
BUT the contents of the boxes have to be in
every program.
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11. An example of program building
Problem: convert distances from miles to
kilometers
Algorithm:
Get the distance
in miles
Convert the distance
to kilometers
(multiply by 1.609)
Display the distance
in kilometers
How to write this in C?
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12. contains info about printf and scanf for the compiler
#include<stdio.h>
int main(void) {
double miles; /*distance in miles */
double kms;/*distance in kilometers*/
/* Get the distance in miles. */
printf("Enter the distance in miles: ");
scanf("%lf", &miles);
/*Convert the distance to kilometers*/
kms = * miles;
/*Display the distance in kilometers*/
printf("That equals %f Kms.\n",kms);
return 0; }
declarations
print on the
screen what is between the quotes
read from
the keyboard
to read
a double
see later
(but don’t forget &)
multiplication
to print
a double
to print
a linefeed
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13. Compilers, Linkers, etc C O .obj file L .c file M I P N I K L E E R R
executable
program
.obj file
.c file
your
program
library (ANSI)
header
(stdio.h)
debugger
Source
code
Object
code
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