1. 240-222 Computer Programming Techniques Semester 1, 1998
1. Introduction to C and UNIX
Objectives of these slides:
introduce C using a few examples
introduce gcc

2. Overview 1. The History of C 2. 1st C Program 3. Compiling C using gcc
4. #include
5. 2nd C Program
6. Memory as Many Boxes
7. 3rd C Program
8. A C Program ‘Skeleton’

3. 1. The History of C (D&D Sec. 1.7)
Martin Richards. No types
BPCL
1967
1970 B
Ken Thompson
1972
Dennis Ritchie Some Types C
Bjarne Stroustrup OOP
C++
1986
ANSI C
The standard. Strong Typing
1989

4. 2. 1st C Program (hello.c)
/* my first program */ #include <stdio.h> int main() { printf("Hello World\n"); return 0; }

5. 3. Compiling using gcc $ gcc hello.c $ a.out Output: Hello World
$ gcc -o hello hello.c $ hello Output: Hello World
$ gcc -Wall -o hello hello.c $ hello Output: Hello World

6. 3.1. Compilation in 4 Stages (Sec. 1.11)
Preprocessing
Compilation
Optimization
Linking

7. 4. #include #include <stdio.h>
This header file contains declarations and function ‘headers’, called function prototypes.
The angled brackets tell the compiler that the file stdio.h is in the directory:
/usr/include

8. Library files are stored in the directory:
stdio.h only contains function ‘headers’; where is the actual code?
At linking time, gcc automatically includes certain standard libraries.
Library files are stored in the directory:
/usr/lib

9. 5. 2nd C program (add.c) Fig. 2.5
/* Addition program */ #include <stdio.h> int main() { int x, y, z; printf("Enter first integer\n"); scanf("%d", &x); printf("Enter second integer\n"); scanf("%d", &y); z = x + y; printf("Sum is %d\n", z); return 0; }

10. Compile and Run
$ gcc -Wall -o add add.c $ add Enter first integer /* I type this */ Enter second integer /* Me again */ Sum is 5 /* Correct! */

11. 6. Memory as Many Boxes Sec. 2.4
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

12. C Programs Mess With Boxes
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

13. 7. 3rd C Program (bigger.c) Fig. 2.13
/* Using the if statement, relational operators and equality operators */ #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);
continued

14. if(a == b) printf("%d is equal to %d\n", a, b); if(a
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

15. 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; }

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

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

18. Compile and Execute:
$ gcc -Wall -o skeleton skeleton.c
$ skeleton