Formatting Output

Formatting Output #include <stdio.h> void main (void) { printf(“Welcome to”); printf(“London!”); printf(“\nHow do we\njump\n\ntwo lines?\n”); printf(“\n”); printf(“It will rain\ntomorrow\n”); }

Output Welcome toLondon! How do we Jump two lines? It will rain tomorrow

What if I want to print a \ or “ printf(“How to print a \\ backslash\n”); printf(“How to print a \” quote\n”);

C String Literals • Anything inside double quotes • Use \ to break string literal across a line printf(“This shows how to break \ a string literal across lines\n”); printf(“This shows how to break “ “a string literal across lines\n”);

More Escape Sequences (2.4) • Consist of a backslash followed by a letter, symbol, or combination of digits • Represents a character that has special meaning or specifies an action

Character Escape Sequences • \0 Null character • \a Alert/bell • \n New Line • \0ddd Octal constant • \xddd Hexadecimal constant • \Xddd Hexadecimal constant

Character Escape Sequences • \\ Display a backslash • \’ Display a single quote • \” Display a double quote • \% Display a percent character • \? Display a question mark

Review of Chapter 2 • Basic structure of a C program • Writing comments • Using character escape sequences • Displaying special characters • C string literals • Basic debugging techniques

Let’s look at L2_5.c

What are the important features of a C program • The main function name must be main • The prog body must start with { • The prog body must end with } • A C statement must end with ; • A C statement is case sensitive • A C statement is location insensitive

More C program features • In general, it is OK to add blank(s) between tokens in a C statement but it is not OK to add blank(s) within a token • C uses character escape sequencs for special characters and action • Make your comments stand out. Do not hide them.

What is debugging • Fixing problems that cause your program to behave unexpectedly. • 3 types of programming errors • Syntax errors • Run-time errors • Logic errors

Syntax Errors • Violation of C “grammer” rules • Typographical mistakes • Compile time errors

Run-time errors • Semantic errors (errors of meaning) • Not detected by compiler • Violation of the rules during execution of your program

Logic errors • Most difficult errors to find • Program compiles and runs fine it just does not produce the correct results. • Is the input data correct?

How to reduce programming errors • Writing your program neatly • Adding blank lines at natural locations • Lining up your opening and closing braces • Add useful comments • Build your program in sections (layers)

How to debug your program • Think about debugging up front before you write your program • Write your program in layers • Look for the obvious syntax errors • Correct function names • Statement termination • Are my parentheses and braces matched up

Lets do a debugging example • Program 2.2 Debugging (Page 64)

Formatting Output