1. Chapter 1 Basic C Programming
1. Introduction to C and UNIX
Objectives of these slides:
Review C Program
Introduce gcc

2. 1st C Program hello.c /* My first C programming */
#include<stdio.h>
int main() {
printf(“Hello World”);
return 0; }

3. Source file Executable file
/* My first C programming */
#include<stdio.h>
int main() {
printf(“Hello World”);
return 0; }
Compile
Link
Executable file

4. Compiling using gcc
$ gcc hello.c //Compile  Output is a.out $ ./a.out //Run Program Hello World
$ gcc -o hello hello.c //Compile  Output is hello $ ./hello Hello World
$ gcc –Wall –o hello hello.c //Compile with warning $ ./hello Hello World
output
output
output

5. 2nd C program add.c /* Addition program */ #include <stdio.h>
int main()
{ int x,y,z;
printf(“Enter first integer: ”);
scanf(“%d”, &x);
printf(“Enter second integer: ”);
scanf(“%d”, &y);
z = x + y;
printf(“Sum is %d \n”, z);
return 0; }

6. Compile and Run $ gcc –Wall –o add add.c
$ ./add Enter first integer: 2
Enter second integer: 3
Sum is 5

7. Memory as Many Boxes
Each box is labelled with an identifier; it is the name of the box.
e.g x, y, z
The address of a box is & and its name
e.g &x, &y, &z;
Boxes are typed (e.g. int, float, etc.). This specifies their size and shape
Boxes contain values (e.g. 5, 3.4)
C Programs Mess With Boxes

8. 3rd C Program bigger.c #include <stdio.h> int main()
{ int a, b; printf(“Enter two integers, and I will tell you the relationships they satisfy: ”); scanf(“%d%d”, &a, &b);
if(a == b) printf("%d is equal to %d\n", a, b); if(a != b) printf("%d is not equal to %d\n", a, b); if(a < b) printf("%d is < than %d\n", a, b);
continued

9. if(a > b) printf("%d is > than %d\n", a, b); if(a <= b) printf("%d is <= to %d\n", a, b); if(a >= b) printf("%d is >= to %d\n", a, b); return 0; }

10. Compile and Run $ gcc –Wall –o bigger bigger.c
$ ./bigger Enter two integers, and I will tell you the relationships they satisfy: 3 7
3 is not equal to 7
3 is < than 7
3 is <= to 7

11. A C Program ‘Skeleton’ /* Name, student no. (E-mail addr.) Date
Description of Code (5-10 lines) */
#include<stdio.h>
int main() {
/* declare some variables */
/* do something */
return 0; }

12. Compile and Execute:
$ gcc –Wall –o skeleton skeleton.c
$ ./skeleton

13. How to Start Writing a Program
Program = Algorithm + Data Structures
Algorithm:
a series of functions, each using a mix of sequencing, branches, loops, recursion and other functions
Data Structures:
they reflect the structure of the data in the Problem Statement
e.g int, float, arrays, struct, etc

14. Consider the input–output requirements
Dissect (‘Pull apart’) the Problem Statement
Use top-down design (also called stepwise refinement)

15. Control Flow Sequence Choice if-else switch-case Loop for while
do-while
Recursion

16. The if statement : scanf(“%d”, &grade); if(grade >= 60)
printf(“Passed \n”);
else {
printf(“Failed \n”);
printf(“Repeat Course \n”); } :

17. : scanf(“%d”, &temp);
if(temp < 0)
setting = setting + 20;
else if(temp < 10)
setting = setting + 10;
else
setting = setting + 1; :

18. The switch statement For multiple choices: c1 c2 c3 task-A task-B
condition
task-A
task-B
task-C c1 c2 c3

19. switch(int-expression) {
case c1: task-A; break;
case c2: task-B; break;
case c3: task-C; break; : }

20. Ex. Counting Letter Grades (switch-case)
#include<stdio.h>
int main() {
int grade;
int acount = 0, bcount = 0, ccount = 0,
dcount = 0, fcount = 0;
printf(“Enter the letter grades.\n”);
printf(“Enter EOF to end.\n”); :
continued

21. while((grade = getchar()) != EOF) {
switch(grade) {
case ‘A’: case ‘a’: ++acount; break;
case ‘B’: case ‘b’: ++bcount; break;
case ‘C’: case ‘c’: ++ccount; break;
case ‘D’: case ‘d’: ++dcount; break;
case ‘F’: case ‘f’: ++fcount; break;
case ‘\n’: case ‘ ‘: break;
default: printf(“Incorrect letter grade entered\n Enter a new grade\n”); break; }
continued

22. printf(“\nThe totals for each letter grade are: \n”);
printf(“A: %d \n”, acount);
printf(“B: %d \n”, bcount);
printf(“C: %d \n”, ccount);
printf(“D: %d \n”, dcount);
printf(“F: %d \n”, fcount);
return 0; }

23. Some Points Very common coding style:
while((grade = getchar()) != EOF)
getchar() reads the next character as an integer and assigns it to grade
EOF is an integer constant representing the end-of-file value. Defined in stdio.h

24. Output from letter grades program
Enter the letter grades.
Enter EOF to end input. A B C C A X Incorrect letter grade entered. Enter a new grade. D
I typed return and ctrl>D
continued

25. Totals for each letter grade were:
B: 1
C: 2
D: 1

26. The while statement sum.c
/* sum between 1 and 10 */
#include<stdio.h>
int main()
{ int i = 1, sum = 0;
while(i <= 10) {
sum = sum + i;
i = i + 1; }
printf(“Sum is %d \n”, sum);
return 0;

27. Compile and run
$ gcc -Wall –o sum sum.c
$ ./sum Sum is 55

28. The for statement int main() test for { int count; continuing initial
#include<stdio.h>
int main()
{ int count;
for(count = 1; count <= 10; count++)
printf(“%d \n”, count);
return 0; }
test for
continuing
initial
value
final value
increment

29. The for is a sort of while
for(expr1; expr2; expr3)
statement;
is equivalent to:
expr1;
while(expr2) {
expr3; }

30. #include<stdio.h> FUNCTION PROTOTYPE int add(int a, int b);
FUNCTIONS IN C
PROGRAMMER DEFINED
FUNCTION
C STANDARD
LIBRARY
INCLUDE HEADER FILE
#include<stdio.h>
FUNCTION PROTOTYPE int add(int a, int b);

31. C Standard Library #include<stdio.h> #include<math.h>
int main() {
printf("%f", sqrt(16.0));
return 0; }
header file
Call function

32. Programmer defined function
/* Finding the maximum of three integers */
#include <stdio.h> int maximum(int x, int y, int z);
int main()
{ int a, b, c;
printf(“Enter three integers: “);
scanf(“%d%d%d”,&a,&b,&c);
printf(“Maximum is %d\n”, maximum(a,b,c));
return 0; }
function prototype
Call function
continued

33. Function definition int maximum(int x, int y, int z)
/*returns the biggest of x, y and z */ {
if(x > y && x > z)
return x;
else if ( y > z)
return y;
else
return z; }

34. Execution
Enter three integers:
Maximum is 85

35. Array
An array is a data structure which can hold a sequence of values.
The array C[ ] holds 3 integer values:
c[0]
c[1]
c[2]
-45 6 72

36. Ex. Array #include<stdio.h> #define SIZE 10 int main()
/* Initialize array s to the even integers from 2 to 20 */
#include<stdio.h>
#define SIZE 10
int main()
{ int s[SIZE], j;
for(j = 0; j < SIZE; j++)
s[j] = * j;
printf(“%s%13s \n”,”Element”, “Value”);
printf(“%7d%13d \n”,j, s[j]);
return 0; }
Typical range
expression

37. Output:
Element Value
0 2
1 4
2 6
: :
9 20

38. Functions using Arrays
/* A Program which illustrates the differences between passing an array to a function and passing an array element */
#include<stdio.h>
#define SIZE 5
void modifyArray(int b[], int size);
void modifyElement(int e); :
continued

39. printf(“The values of the original array are: \n”);
int main() {
int a[SIZE] = {0,1,2,3,4};
int i;
printf(“The values of the original array are: \n”);
for(i = 0; i<SIZE; i++)
printf(“%3d”, a[i]);
printf(“\n”); :
continued

40. continued modifyArray(a, SIZE);
printf(“The values of the modified array are: \n”);
for(i=0; i<SIZE; i++)
printf(“%3d”, a[i]);
printf(“\n”);
printf(“The value of a[3] is %d\n”,a[3]);
modifyElement(a[3]);
printf(“The value of a[3] is %d\n”, a[3]);
return 0; }
continued

41. void modifyArray(int b[], int size) { int j; for(j=0; j<size; j++)
b[j] *= 2; }
void modifyElement(int e) {
printf(“Value in modifyElement is %d\n”, e*=2);

42. Passing Arrays to Functions
The call to the function modifyArray() is:
modifyArray(a, SIZE);
C treats array arguments differently .
Any changes to the elements of a[] will be retained when the function returns.
This is call by reference.

43. Output: The values of the original array are: 0 1 2 3 4
The values of the modified array are:
The value of a[3] is 6
Value in modifyElement is 12

44. What is a String?
A string is a sequence of characters which end with the NULL character ‘\0’.
e.g.
“Hello”
“ Call”
“9”

45. Use: char color[] = “blue”; Or equivalence :

46. String Manipulation Copy a string: strcpy()
Concatenating strings: strcat()
Comparing strings: strcmp()
Searching a string: strchr()
String Length: strlen()

47. Copying a string: strcpy()
#include<stdio.h>
#include<string.h>
int main() {
char x[]=“Happy birthday to you”;
char y[25];
printf(“String in x is: %s\n
String in y is: %s\n”,
x, strcpy(y,x));
return 0; }

48. Output: Function prototype in string.h:
String in x is Happy Birthday to You String in y is Happy Birthday to You
Function prototype in string.h:
char *strcpy(char *s1, const char *s2);

49. Comparing Strings: strcmp()
int strcmp(const char *s1, const char *s2);
Compares the string s1 to the string s2
Returns
<0 if s1 < s2
0 if s1 == s2
>0 if s1 > s2

50. Using strcmp() #include<stdio.h> #include<string.h>
int main()
{ char s1[] = “Happy New Year”;
char s2[] = “Happy New Year”;
char s3[] = “Happy Holidays”;
printf(“%s%s\n %s%s\n %s%s\n
%s%2d\n %s%2d\n %s%2d\n”,
“s1 = ”,s1,“s2 = ”,s2,“s3 = ”,s3,
“strcmp(s1,s2) = ”,strcmp(s1,s2),
“strcmp(s1,s3) = ”,strcmp(s1,s3),
“strcmp(s3,s1) = ”,strcmp(s3,s1),
return 0; }

51. Output: s1 = Happy New Year s2 = Happy New Year s3 = Happy Holidays
strcmp(s1,s2) = 0
strcmp(s1,s3) = 6
strcmp(s3,s1) = -6

52. Coding strcmp() The array version:
int strcmp(const char *s, const char *t)
{ int i;
for(i=0; s[i] == t[i]; i++)
if(s[i] == ‘\0’)
return 0;
return s[i] – t[i]; }

53. Searching a String: strchr()
#include <stdio.h> #include <string.h> int main() { char *rest, *sh = "Hello"; char c = 'l'; rest = strchr(sh, c); printf("%s", rest); /* gives llo */ return 0; }

54. Function prototype in string.h:
‘l’
‘o’
‘\0’ sh
rest
Function prototype in string.h:
char *strchr(const char *s, int c);