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Introduction to C
Tom Chao Zhou
CSC2100B Data Structures Tutorial 1

Outline
? Information
? Introduction to C
? Basics
? If Statement
? Loops
? Functions
? Switch case
? Pointers
? Structures
? File I/O

Information
? Your TA Team:
? Jianye Hao
? jyhao AT cse.cuhk.edu.hk
? Tom Chao Zhou
? czhou AT cse.cuhk.edu.hk
? Xin Xin
? xxin AT cse.cuhk.edu.hk
? Haifeng Wan
? hfwan AT cse.cuhk.edu.hk

Information
? Course Information:
? Web Page:
? http://wiki.cse.cuhk.edu.hk/irwin.king/teaching/csc2100b/2010
? Tutorial Page:
? http://wiki.cse.cuhk.edu.hk/irwin.king/teaching/csc2100b/tutorials
? Anti-plagiarism Policy:
? http://www.cuhk.edu.hk/policy/academichonesty/

Information
? Assignment
? There will be both written and programming parts in assignments.
? Written part: submit to the assignment box in 10/F SHB.
? Programming part: via Online Judge systems. (Will be introduced next week)
? You will receive your login Id for CSC2100B online judge via your
sxxxxxxx@mailserv.cuhk.edu.hk email account. (A few days later).
? Keep it safe and do not disclose it.

Introduction to C
? Basics
? If Statement
? Loops
? Functions
? Switch case
? Pointers
? Structures
? File I/O

Introduction to C: Basics
//a simple program that has variables
#include <stdio.h>
int main()
{
int x; //(32 bits)
char y; //(8 bits)
float z; //(32 bits)
double t; //(64 bits)
printf(��hello world��n��);
int test; //wrong, The variable declaration must appear first
return 0;
}

Introduction to C: Basics
//reading input from console
#include <stdio.h>
int main()
{
int num1;
int num2;
printf( "Please enter two numbers: " );
scanf( "%d %d", &num1,&num2 );
printf( "You entered %d %d", num1, num2 );
return 0;
}

Introduction to C: if statement
#include <stdio.h>
int main()
{
int age; /* Need a variable... */
printf( "Please enter your age" ); /* Asks for age */
scanf( "%d", &age ); /* The input is put in age */
if ( age < 100 )
{ /* If the age is less than 100 */
printf ("You are pretty young!n" ); /* Just to show you it works... */
}
else if ( age == 100 )
{ /* I use else just to show an example */
printf( "You are oldn" );
}
else
{
printf( "You are really oldn" ); /* Executed if no other statement is*/
} return 0;
}

Introduction to C: Loops(for)
#include <stdio.h>
int main()
{
int x;
/* The loop goes while x < 10, and x increases by one every loop*/
for ( x = 0; x < 10; x++ )
{
/* Keep in mind that the loop condition checks
the conditional statement before it loops again.
consequently, when x equals 10 the loop breaks.
x is updated before the condition is checked. */
printf( "%dn", x );
}
return 0;
}

Introduction to C: Loops(while)
#include <stdio.h>
int main()
{
int x = 0; /* Don't forget to declare variables */
while ( x < 10 )
{ /* While x is less than 10 */
printf( "%dn", x );
x++; /* Update x so the condition can be met eventually */
}
return 0;
}

Introduction to C: Loops(do while)
#include <stdio.h>
int main()
{
int x;
x = 0;
do
{
/* "Hello, world!" is printed at least one time
even though the condition is false*/
printf( "%dn", x );
x++;
} while ( x != 10 );
return 0;
}

Introduction to C: Loops(break and
continue)
#include <stdio.h>
int main()
{
int x;
for(x=0;x<10;x++)
{
if(x==5)
{
break;
}
printf("%dn",x);
}
return 0;
}
#include <stdio.h>
int main()
{
int x;
for(x=0;x<10;x++)
{
if(x==5)
{
continue;
}
printf("%dn",x);
}
return 0;
}
0
1
2
3
4
0
1
2
3
4
6
7
8
9

Introduction to C: function
#include <stdio.h>
//function declaration
int mult ( int x, int y );
int main()
{
int x;
int y;
printf( "Please input two numbers to be multiplied: " );
scanf( "%d", &x );
scanf( "%d", &y );
printf( "The product of your two numbers is %dn", mult( x, y ) );
return 0;
}
//define the function body
//return value: int
//utility: return the multiplication of two integer values
//parameters: take two int parameters
int mult (int x, int y)
{
return x * y;
}

#include <stdio.h>
//function declaration, need to define the function body in other places
void playgame();
void loadgame();
void playmultiplayer();
int main()
{
int input;
printf( "1. Play gamen" );
printf( "2. Load gamen" );
printf( "3. Play multiplayern" );
printf( "4. Exitn" );
printf( "Selection: " );
scanf( "%d", &input );
switch ( input ) {
case 1: /* Note the colon, not a semicolon */
playgame();
break; //don't forget the break in each case
case 2:
loadgame();
break;
case 3:
playmultiplayer();
break;
case 4:
printf( "Thanks for playing!n" );
break;
default:
printf( "Bad input, quitting!n" );
break;
}
return 0;
}
switch
case

Introduction to C: pointer variables
? Pointer variables are variables that store memory addresses.
? Pointer Declaration:
? int x, y = 5;
? int *ptr;
? /*ptr is a POINTER to an integer variable*/
? Reference operator &:
? ptr = &y;
? /*assign ptr to the MEMORY ADDRESS of y.*/
? Dereference operator *:
? x = *ptr;
? /*assign x to the int that is pointed to by ptr */

Introduction to C: pointer variables

#include <stdio.h>
//swap two values
void swap(int* iPtrX,int* iPtrY);
void fakeswap(int x, int y);
int main()
{
int x = 10;
int y = 20;
int *p1 = &x;
int *p2 = &y;
printf("before swap: x=%d y=%dn",x,y);
swap(p1,p2);
printf("after swap: x=%d y=%dn",x,y);
printf("------------------------------n");
printf("before fakeswap: x=%d y=%dn",x,y);
fakeswap(x,y);
printf("after fakeswap: x=%d y=%d",x,y);
return 0;
}
void swap(int* iPtrX, int* iPtrY)
{
int temp;
temp = *iPtrX;
*iPtrX = *iPtrY;
*iPtrY = temp;
}
void fakeswap(int x,int y)
{
int temp;
temp = x;
x = y;
y = temp;
}

Introduction to C: struct
#include <stdio.h>
//group things together
struct database {
int id_number;
int age;
float salary;
};
int main()
{
struct database employee;
employee.age = 22;
employee.id_number = 1;
employee.salary = 12000.21;
}

//content in in.list
//foo 70
//bar 98
//biz 100
#include <stdio.h>
int main()
{
FILE *ifp, *ofp;
char *mode = "r";
char outputFilename[] = "out.list";
char username[9];
int score;
ifp = fopen("in.list", mode);
if (ifp == NULL) {
fprintf(stderr, "Can't open input file in.list!n");
exit(1);
}
ofp = fopen(outputFilename, "w");
if (ofp == NULL) {
fprintf(stderr, "Can't open output file %s!n", outputFilename);
exit(1);
}
while (fscanf(ifp, "%s %d", username, &score) == 2) {
fprintf(ofp, "%s %dn", username, score+10);
}
fclose(ifp);
fclose(ofp);
return 0;
}
mode:
r - open for reading
w - open for writing (file need not exist)
a - open for appending (file need not exist)
r+ - open for reading and writing, start at beginning
w+ - open for reading and writing (overwrite file)
a+ - open for reading and writing (append if file
exists)
File I/O

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