Intro to Art of Programming

1. B Smith: Slightly long. Score 3. B Smith: 8/24/05: Steps are not small enough. Introduction of loop code, etc., is confusing. Must find a better point of entry. Intro to Art of Programming Math 130Lecture # 01

2. Overview • Programs and their connection to algorithms • Compilation • Pseudocode: The alternative to thinking in C • Modularity • The components of a program • main() • functions/subroutines/procedures • A simple program • Hello World

3. Programming - B. Gates • Interviewer: "Is studying computer science the best way to prepare to be a programmer?" • Bill Gates: "No, the best way to prepare is to write programs, and to study great programs that other people have written. In my case, I went to the garbage cans at the Computer Science Center and I fished out listings of their operating system."

4. What is a Program? • A computer program is... • A list of instructions • A sequence of operations • Commands to a computer • Something that accepts input, and manipulates it to get an output. • The output to this one is… #include <stdio.h> void findMax(int [5]); int main() { int nums[5] = {2, 18, 1, 27, 16}; findMax(nums); return 0; } void findMax(int vals[5]) { int i, max = vals[0]; for (i = 1; i <= 4; ++i) if (max < vals[i]) max = vals[i]; printf("The max value is %d", max); getchar(); return; }

5. Programming Language • The allowed group of instructions • Some instructions are built from other instructions • findMax() • Others are requested from an established group, or library of instructions (library functions) • printf() • getchar() #include <stdio.h> void findMax(int [5]); int main() { int nums[5] = {2, 18, 1, 27, 16}; findMax(nums); return 0; } void findMax(int vals[5]) { int i, max = vals[0]; for (i = 1; i <= 4; ++i) if (max < vals[i]) max = vals[i]; printf("The max value is %d", max); getchar(); return; }

6. #include <stdio.h> void findMax(int [5]); int main() { int nums[5] = {2,18,1,27}; findMax(nums); return 0; } 111111000111 111111011010 111101011110 110101000110 100101011010 101111000110 111001011011 110001010000 100001011010 101001011011 110001000111 001001011011 111001011010 111001011010 111111011010 111001011010 source code machine code Basics of Program Development • The process starts with a text file (C language) and ends with a .exe (executable file, “Machine Language”) • machine language is understood by the computer • Six phases before a program is executed: • edit • pre-process • compile • link • load • execute

7. Compiling Programs • Edit a file and save with the proper extension • .c for C language, .cpp for C++, .java for Java • this file must be saved as a “text” file, not a word document • Give the command to compile the program • the preprocessor does additional prep work on source • the source code gets translated to machine code • Your code is linked with other resources/library functions • The linked code is loaded into computer memory and executed

8. Pseudocode • Simple language to help a programmer “think through” a program before writing in a programming language like C • Consists mainly of action statements • Use standard English, Spanish, Czech, etc. for expressing the flow of operations and computations • Not executed on computers • Using pseudocode is a must for many programmers • Many people think better with pen and paper vs. at the computer

9. B Smith: More useful to think of this as numbers coming out of a black box. We only see numbers one ata time. Pseudocode Example • Describe an algorithm to find the maximum number in the list of numbers {2, 18, 1, 27, 16} • select the first number and name it “max” • point to “next number” • reassign “max” with next on list if it’s greater than current max • if not at end of list, go to step 2 void findMax(int vals[5]) {. . . max = vals[0]; for (i = 1; i <= 4; ++i) if (max < vals[i]) max = vals[i]; printf("The max value is %d", max); }

10. Modularity • Def of a module: • A “bite-sized” chunk of code can be called a module. Typically each module has a distinct purpose. • Makes troubleshooting (debugging) programs much easier • Modules in C are generally implemented with functions #include <stdio.h> void findMax(int [5]); int main() { int nums[5] = {2, 18, 1, 27, 16}; findMax(nums); return 0; } void findMax(int vals[5]) { int i, max = vals[0]; for (i = 1; i <= 4; ++i) if (max < vals[i]) max = vals[i]; printf("The max value is %d", max); getchar(); return; }

11. Basic Structure of a C Program output “Hello World!” Example: Hello World Algorithm: C Program: #include <stdio.h> int main() { printf(“HelloWorld!”); return 0; }

12. The main() function • Consider main( ) to be a driver function. • The chief of the submodules • All programs require a main function • Example: • Helps you think about top-down programming int main() { GETgrossPay( ); DetTaxes( ); CalNetPay( ); displyAns( ); return 0; }

13. The printf() function • printf() is a prewritten function in C • It writes formatted output to the standard output • typically the screen/terminal #include <stdio.h> int main() { printf("Hello there world!"); return 0; }

14. Comments • A comment is anything you want the compiler to ignore in the process of reading and creating your program • /* is the beginning of a comment • */ is the end of a comment • They do not have to be on the same line • Each beginning must be matched with an end • Use comments liberally! • They will tell you (or others) what you thought you were doing; i.e., the intent of the code • Very, very important for documenting your thoughts!

15. Comments (cont) • Comments do not “nest” /*Comments start with a “/*” and end with a “*/” but they don’t nest! */

16. Preprocessor Commands • #include <stdio.h> is a preprocessor command • Preprocessor commands always start with # • They specify an action to be taken prior to the compiler translating the source code into machine code • The statement here does literally what it says: include the file “stdio.h” prior to compiling. • stdio.h is defined as a “header file” • We need stdio.h to be able to use printf ( ) /* File: Lab01.c Description: Display hello! Programmer: I. Student Date: 1/24/05 */ #include <stdio.h> int main() { printf("Hello!"); return 0; }

17. The first program • Enter, compile, run and submit this program: • under Dev-C: Alt-Insert-Comment/header /* File: Lab01.c Description: Displays Hello there world! Programmer: I. Student Date: 1/20/06 */ #include <stdio.h> #include <stdlib.h> int main() { printf("Hello there world!"); system(“pause”); return 0; }

18. Review • Programs and their connection to algorithms • Compilation • Pseudocode: The alternative to thinking in C • Modularity • The components of a program • main() • functions/subroutines/procedures • A simple program • Hello World