Java: An Introduction to Problem Solving and Programming (8th Edition)
8th Edition
ISBN: 9780134462035
Author: Walter Savitch
Publisher: PEARSON
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Textbook Question
Chapter 4, Problem 8E
Write a loop that will count the number of blank characters in a given string.
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Students have asked these similar questions
The next problem concerns the following C code:
/copy input string x to buf */
void foo (char *x) {
char buf [8];
strcpy((char *) buf, x);
}
void callfoo() {
}
foo("ZYXWVUTSRQPONMLKJIHGFEDCBA");
Here is the corresponding machine code on a Linux/x86 machine:
0000000000400530 :
400530:
48 83 ec 18
sub
$0x18,%rsp
400534:
48 89 fe
mov
%rdi, %rsi
400537:
48 89 e7
mov
%rsp,%rdi
40053a:
e8 di fe ff ff
callq
400410
40053f:
48 83 c4 18
add
$0x18,%rsp
400543:
c3
retq
400544:
0000000000400544 :
48 83 ec 08
sub
$0x8,%rsp
400548:
bf 00 06 40 00
mov
$0x400600,%edi
40054d:
e8 de ff ff ff
callq 400530
400552:
48 83 c4 08
add
$0x8,%rsp
400556:
c3
This problem tests your understanding of the program stack. Here are some notes to
help you work the problem:
⚫ strcpy(char *dst, char *src) copies the string at address src (including
the terminating '\0' character) to address dst. It does not check the size of
the destination buffer.
• You will need to know the hex values of the following characters:
Consider the following assembly code for a C for loop:
movl $0, %eax
jmp
.L2
.L3:
addq
$1, %rdi
addq
%rsi, %rax
subq
$1, %rsi
.L2:
cmpq
%rsi, %rdi
jl
.L3
addq
ret
%rdi, %rax
Based on the assembly code above, fill in the blanks below in its corresponding C
source code. Recall that registers %rdi and %rsi contain the first and second, respectively,
argument of a function. (Note: you may only use the symbolic variables x, y, and
result in your expressions below do not use register names.)
long loop (long x, long y)
{
long result;
}
for (
}
return result;
__; y--) {
In each of the following C code snippets, there are issues that can prevent the compiler
from applying certain optimizations. For each snippet:
Circle the line number that contains compiler optimization blocker.
⚫ Select the best modification to improve optimization.
1. Which line prevents compiler optimization? Circle one: 2 3 4 5 6
Suggested solution:
⚫ Remove printf or move it outside the loop.
Remove the loop.
• Replace arr[i] with a constant value.
1 int sum (int *arr, int n) {
2
int s = 0;
3
for (int i
=
0; i < n; i++) {
4
5
6
}
7
8 }
s = arr[i];
printf("%d\n", s);
return s;
234206
2. Which line prevents compiler optimization? Circle one: 2 3 4 5 6
Suggested solution:
Move or eliminate do_extra_work() if it's not necessary inside the loop.
Remove the loop (but what about scaling?).
⚫ Replace arr[i] *= factor; with arr[i] = 0; (why would that help?).
1 void scale (int *arr, int n, int factor) {
5
6 }
for (int i = 0; i < n; i++) {
rr[i] = factor;
do_extra_work ();
Chapter 4 Solutions
Java: An Introduction to Problem Solving and Programming (8th Edition)
Ch. 4.1 - What output is produced by the following code? int...Ch. 4.1 - Can the body of a while loop execute zero times?...Ch. 4.1 - What output is produced by the following code? int...Ch. 4.1 - Revise the following code so that it uses a while...Ch. 4.1 - What output is produced by the following code? int...Ch. 4.1 - Imagine a program that reads the population of a...Ch. 4.1 - Prob. 7STQCh. 4.1 - What output is produced by the following code? int...Ch. 4.1 - What output is produced by the following code? for...Ch. 4.1 - What output is produced by the following code? for...
Ch. 4.1 - Prob. 11STQCh. 4.1 - Write a for statement that displays the even...Ch. 4.1 - Prob. 13STQCh. 4.2 - Write a Java loop that will display the phrase One...Ch. 4.2 - Write a Java loop that will set the variable...Ch. 4.2 - Write a Java loop that will read a list of numbers...Ch. 4.2 - What output is produced by the following code? for...Ch. 4.2 - What output is produced by the following code? for...Ch. 4.2 - What output is produced by the following code? for...Ch. 4.2 - Revise the loop shown in Listing 4.6 to use a...Ch. 4.2 - What is the bug in the code in the section Tracing...Ch. 4.2 - Add some suitable output statements to the...Ch. 4.2 - What is the bug in the code in the previous...Ch. 4.2 - Prob. 24STQCh. 4.2 - Suppose that you did not have assertion checking...Ch. 4.3 - Prob. 26STQCh. 4 - Write a fragment of code that will read words from...Ch. 4 - Develop an algorithm for computing the...Ch. 4 - Develop an algorithm for a simple game of guessing...Ch. 4 - Write a fragment of code that will compute the sum...Ch. 4 - Convert the following code so that it uses nested...Ch. 4 - Write a for statement to compute the sum 1 + 22 +...Ch. 4 - (Optional) Repeat the previous question, but use...Ch. 4 - Write a loop that will count the number of blank...Ch. 4 - Write a loop that will create a new string that is...Ch. 4 - Write a program that will compute statistics for...Ch. 4 - Suppose we attend a party. To be sociable, we will...Ch. 4 - Define an enumeration for each of the months in...Ch. 4 - Write a fragment of code that computes the final...Ch. 4 - Suppose that you work for a beverage company. The...Ch. 4 - Suppose that we want to compute the geometric mean...Ch. 4 - Prob. 16ECh. 4 - Create an applet that draws a pattern of circles...Ch. 4 - Prob. 18ECh. 4 - What does the following fragment of code display?...Ch. 4 - Repeat Practice Program 4 of Chapter 3, but use a...Ch. 4 - Write a program that implements your algorithm...Ch. 4 - Repeat Practice Program 5 of Chapter 3, but use a...Ch. 4 - Write a program to read a list of nonnegative...Ch. 4 - Write a program to read a list of exam scores...Ch. 4 - Combine the programs from Programming Projects 5...Ch. 4 - Write a program that simulates the Magic 8 Ball...Ch. 4 - Whats for dinner? Let the computer decide. Write a...Ch. 4 - Write a program that implements your algorithm...Ch. 4 - Prob. 2PPCh. 4 - Write a program that reads a bank account balance...Ch. 4 - Modify Programming Project 5 from Chapter 2 to...Ch. 4 - Write a program that asks the user to enter the...Ch. 4 - Write a program that simulates a bouncing ball by...Ch. 4 - You have three identical prizes to give away and a...Ch. 4 - Prob. 9PPCh. 4 - Holy digits Batman! The Riddler is planning his...Ch. 4 - Your country is at war and your enemies are using...Ch. 4 - Prob. 12PPCh. 4 - Prob. 13PPCh. 4 - Prob. 14PPCh. 4 - (Challenge) Repeat the previous project, but...Ch. 4 - Write a JavaFx application that displays a series...
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