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Computers in Engineering
Pseudocode and C Language
Review
Pseudocode
z Pseudocode is an artificial and informal language
that helps you develop algorithms.
z Pseudocode is similar to everyday English; it is
convenient and user friendly although it is not an
actual computer programming language.
z Pseudocode programs are not executed on
computers. Rather, they merely help you "think out"
a program before attempting to write it in a
programming language such as C.
z Pseudocode consists purely of characters, so you
may conveniently type pseudocode programs into a
computer using an editor program.
Pseudocode
z Carefully prepared pseudocode programs may be
converted easily to corresponding C programs.
z Pseudocode consists only of action statements-
those that are executed when the program has been
converted from pseudocode to C and is run in C.
Definitions are not executable statements. They are
messages to the compiler.
z Each variable should be listed and the purpose of
each should be briefly mentioned at the beginning of
the pseudocode program.
Guide for Pseudocode
- State your name
- State the date
- State the name of the subroutine.
- Give a brief description of the function of the subroutine/program.
- State the names of the input variables, their types, and give a brief description for each.
- St tState the names of the output variables, their types, and give a brief th f th t t i bl th i t d i b i f description for each.
- Give a list of instructions with enough detail that someone can translate the pseudocode into a computer language such as C, C++, Java, etc. Note, your pseudocode should paraphrase your algorithm and not look identical to C code.
- Your pseudocode should be indented just like when you write your program. You should use {} or if/else/endif (for/endfor, while/endwhile, etc.) syntax to denote the start and end of blocks of statements.
Example Pseudocode
- Programmer: Gary E. Christensen
- Date: 8/20/
- Name: print_matrix
- Function: Print matrix nicely to screen.
- Input: a[] = single subscripted int array of size arow * acol = matrix to be printed.
- arow = int = number of rows of matrix a.
- acol = int = number of columns of matrix a.
- MAXSIZE = global constant that specifies the maximum size of the array
- Output: matrix a[] printed to the screen.
- Algorithm:
- // Check for error conditions
- if (arow <= 0) or (acol <= 0) then print error message and return endif
- if (arow * acol > MAXSIZE) then print error message and return endif
- // Print the matrix
- k = 0
- for i = 0 to arow - 1
- print bar '|'
- for j = 0 to acol - 1
- print a[k] right justified
- k = k + 1
- endfor
- print bar '|' followed by a newline
- endfor
Documentation
/******************************************************************
- Programmer: *
- Date: <Today's date> *
z The main program and each subroutine must be
documented.
- Name: *
- Function: *
- Algorithm: *
- Input: <Name each input variable to the function on a separate *
- line and give a description of what it is> *
- Output: <Name each output variable on a separate line and *
- give a description of what it is> *
******************************************************************/
Example Documentation
/*****************************************************************
- Programmer: Gary Christensen *
- Date: 2/17/04 *
- Name: quicksort *
- Function: This function sorts an array of integers from *
- smallest to largest value. *
- Algorithm: This subroutine sorts a list of integers using *
- recursion. The first element of the list is moved to * ** itits fifinal l positioniti iin ththe li tlist andd a sublistbli t off numbersb **
- less than this number and a sublist of numbers greater *
- than this number is created. Each sublist is then *
- sorted by passing it to quicksort again. The *
- termination condition for the recursion are as *
- follows: A one element list is sorted by definition and *
- is returned. *
- Input: ListOfInts - a pointer to an array of integers to be *
- sorted. *
- size - the number of integers in the list to be sorted. *
- Output: ListOfInts - a pointer to an array of sorted integers *
*****************************************************************/
If statement
scanf(“%d”,&x); if ((x < 0)||(x>5)){ printf(“Please enter an integer between 0 and 5.\n”); printf(“Try again\n”); scanf(“%d”,&x); }
Use & to read integer into variable
Logical OR Operator
if (score >= 60){ printf(“You Passed\n); }else{ printf(“You Failed\n”); };
Logical Expressions
((x <= 5)&&(x >= 0)) and (y != 5) are examples of logical expressions.
Logical AND Operator
Logical NOT Equal Operator
Relational Operators
== Equality (don’t confuse with the
assignment operator, =)
!= not equal
greater thant th
< less than
= greater than or equal
<= less than or equal
Compound Conditions
z Logical Operators:
&& Logical And
|| Logical Or
! Not (complement)
if ((score > 100) || (score < 0)){
printf(“Score is invalid\n”);
if (!((score <= 100) && (score >= 0))){
printf(“Score is invalid\n”);
If-else statement
if (score == 100) printf(“Your grade is an A+\n); else if (score >= 95) printf(“Youri grade iis an A\n”);
else if (score >= 90) printf(“Your grade is an A-\n”); else printf(“Your grade is lower than an A-\n”); . . .
The Switch Statement
z Multiple-selection structure
z Good for algorithms containing a
series of decisions
z – Every constant integral value tested
z – Different actions for each value
z Consists of
z case labels and default case
Class Average Example
z Problem statement: A class of ten students
took a quiz. The grades (integers in the range 0 to 10) for this quiz are available to you. Determine the class average on the quiz.
z class average = (sum of grades / total
students)
z Main algorithm:
input each of the grades
perform the averaging calculation
print the result
Pseudo-code Algorithm
Set total to zero
Set grade counter to one
while (grade counter is less than or equal to ten):
Input the next grade
Add the grade into the total
Add one to the grade counter
endwhile
Set the class average to the total divided by ten
Print the class average
Note: This is an example of a counter-controlled loop (loop is executed a fixed number of times, controlled by a counter)
C Program For the Example
/* average program, counter controlled repetition / #include <stdio.h> int main() { / note meaningful variable names / int counter, grade, total, average; / INITIALIZATION phase */ total = 0; counter = 1;
include stdio.h for printing and reading variables beginning of main program
/* PROCESSING phase: loop for average calculations/ while (counter <= 10) { printf("Enter grade: "); scanf("%d", &grade); total = total + grade; counter = counter + 1; } / end while / / TERMINATION phase */ average = total / 10; printf("Class average is %d\n", average); return 0; }
Sentinel-controlled loops
z Sentinel value : a special input value to indicate the end of data entry
z Also called a flag value or signal value
z The user must enter the sentinel value to indicate that all data items have been entered
z Used in cases of indefinite repetition
z Number of data items to be processed is not
known before the loop begins executing
Class Average Example Using a
Sentinel (Pseudo-code)
Initialize total to zero Initialize counter to zero Input the first grade while (the user has not yet entered the sentinel): Add this grade into the running total Add one to the grade counterAdd one to the grade counter Input the next grade (possibly the sentinel) endwhile If the counter is not equal to zero: Set the average to the total divided by the counter Print the average else Print “No grades were entered” endif
double average = 0.0; /* new data type / int counter = 0; int grade =0; int total = 0; / INITIALIZATION phase / printf("Enter grade, -1 to end: "); scanf("%d", &grade); /Loop to perform summation*/ while (grade != -1) { total = total + grade; counter = counter + 1;
/* average program, sentinel-controlled repetition */ #include <stdio.h> int main(){ new data type (double) initializers for variable declarations
printf("Enter grade, -1 to end: "); scanf ("%d", &grade); } /* TERMINATION PHASE / if (counter != 0) { / Casting to avoid integer division/truncation / average = ((double) total) / counter; printf("Class average is %.2f\n", average); } else { printf("No grades were entered\n"); } return 0; / program ended successfully */
}
type cast precision control for format specifier
The for Loop Construct
z Handles some of the counter-controlled repetition details z Example:
for (counter = 0; counter < 10; counter++) { printf("%d\n", counter); }
z for loop has three parts: z initializer z condition z update z Any for loop could be re-written as a while loop (counter- controlled repetition).
for loop versus while loop
for (expression_1; expression_2; expression_3) { statement; }
IS THE SAME AS:IS THE SAME AS:
expression_1; while (expression_2) { statement; expression_3; }
More for Loop Examples
How many times does each loop run?
1. for (j = 1; j <= 100; j++)
2. for (j = 100; j >= 1; j--)
33. for (jfor (j == 7; j7; j <=<= 77; j77; j +=+= 7)7)
4. for (j = 20; j >= 2; j -= 2)
5. for (j = 2; j <= 20; j += 3)
6. for (j = 99; j >= 0; j -= 11)
do/while Loop Construct
z Tests loop-continuation at the end of loop body z Syntax: do { statement1; statement2;; } while (condition); z Example: What does this print? int counter = 1; do { printf("%d", counter); counter++; } while (counter <= 10); /Note semicolon/
do/while Versus while Loop
condition?
False
True
Action
Action
True
while/do do/while
condition?
False
True
for & while statements #define NUM 5
main(){ int i, a[NUM]={4, 2, 7, 3, 9};
/* Print out the elements of array a[] */ for(i=0; i<NUM; i++){ printf(“a[%d]=%d\n”,i,a[i]); }
Define global constants in Caps Only have to change one place no semi colon at end
/* Read in integers into the array a[] */ i=0; while (i<NUM) { scanf(“%d”,&(a[i])); i++; }
/* Print out elements of array a[] */ i=0; do { printf(“a[%d]=%d\n”,i,a[i]); i++; }while(i<NUM); }
Use & and () to read in data into array
Use do-while structure to execute command before checking condition.
