Introduction Chapter 1 1/22/16

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Today's Topics Output Parts of a C Program Comments Input Algorithms Errors and Warnings

Output printf function is used to display output. Must include the i/o library in the program. #include Now the printf function can be used. printf(“%d tons\n", 16);  Output: 16 tons  %d is format for integers.  Where tons is printed.

Displaying Text \n is a new line character If it is not there, the next output will continue on the same line. printf("Without Dennis Ritchie "); printf("there would be no\n"); printf("Steve Jobs.\n");

A Simple C Program A program is needed to figure out how many pets we have, given the number of dogs and cats that includes. Write a program to set the number of cats and dogs. Output the number of pets. The instructions in a program are called code. Here is the code: Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

#include //Program to add up the number of pets int main(void){ int cats = 4; int dogs = 3; int pets = cats + dogs; printf("We have %d pets\n", pets); return 0; }

A Simple C Program main function Where the execution begins. int main(void){ } Block begins and ends with brace { … } Statements within block end with a ;  Tell processor what to do. Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

Assignment Statement int cats = 4; int cats declares a variable. o A variable is a memory location. o Memory is a place to store values temporarily. cat = 4; sets cats to 4. int pets = cats + dogs; o D oes the addition on the right first. o Assigns the answer to pets.

Comments Documents the program Comments Begin line with double slash //  Ends with the end of the line. Span multiple lines between slash-star combination. /* */ Imagine! Java: Programming Concepts in Context by Frank M. Carrano, (c) Pearson Education - Prentice Hall, 2010

return Statement return 0; Ends the program and gives control back to operating system.

Questions What happens when a “\n” is put in the output? Where do the statements in a C program belong? Give an example of an assignment statement.

Input

Input Makes Program Useful Programs so far do one calculation  Example in dogyrs.c More useful if you can input human_yrs  doginput.c

scanf scanf("%d", &human_yrs); scanf – function name “%d” - input format, same as printf formats & -- “address of” operator &human_yrs – where data will be stored.

scanf Execution pauses until user enters a value and hits Value input stored in variable(s)‏ Prompt is recommended  printf to tell user input is expected.  I'll put one in doginput.c #include makes scanf available.

Find the Number of People Write a program to figure how many people are touring Yosemite Park today. Ask for the number of people one tour bus can hold and the number of buses in the park. Output the total number of passengers.

#include int main(void){ //Ask for the number of people on each bus int peopleOnBus; printf("People on one bus?"); scanf("%d", &peopleOnBus); //Ask for the number of buses int noBuses; printf("Number of Buses?"); scanf("%d", &noBuses); //Find total number of people int people = peopleOnBus * noBuses; //Output total number of people printf("%d people\n", people); return 0; }

Login and Password If you don't have a login, send me . Contact me if you forget your password. Change your password to something easy to remember.  ssh -Y onyx  Login again  passwd  Nothing shows while you are typing.

Questions What statement is used to handle input? What preprocessor directive must be in programs that have input or output?

Number of Meals Needed A coding conference provides three meals for each participant. Write a program to input the number of participants then output the total number of meals needed. Write an algorithm with a partner Along with your partner, code the program using vim. – Print it and hand in a copy with both names on it.

Errors and Warnings

Errors Syntax Error  Violation of programming language rules.  Caught by compiler.  Program will not compile. Logic Error  Error while program runs.  For example, incorrect computation. distance = rate/time;

Errors and Warnings Error prevents program from compiling Warning means something might be wrong.  Try to get rid of it.

Questions What kind of error is it? 1.The compiler prints an error message because a semicolon(;) is missing. 2. A program to convert Fahrenheit to Celcius gives incorrect results. 3. The program compiles but the compiler gives a message about a possible problem.