Transcript Power Point Version

Notes About Boolean Expressions
• No boolean type, so boolean expressions
evaulate to 0(false) or 1(true).
– x = (x > y); // is valid. It will set x to 0 or 1.
– if (x) x++; // is valid. If x isn’t 0, it adds 1 to x.
– !!5 // is equal to 1
• For these reasons, try to use boolean
expressions ONLY where they are meant
to be used.
Short-Circuit Evaluation
• AND (&&)
– If the first component is false, the second is never
evaluated
– if (b !=0 && (a/b > 0)) … // If b is zero, we never try to
divide by it
• OR (||)
– If the first component is true, the second is never
evaluated
– if (age >= 21 || fakeid == 1) … // If you are older than
21, you don’t need to check for the fake!
Block of Statements/ Empty
Statement
• A block of statements ({}) acts as a single
statement for syntactic purposes, which is why
we use a block for a part of an if statement
• An empty statement is as follows: ; This is
important because if you add a semicolon
somewhere, it changes the interpretation of the
statement
– if (b !=0); value = a/b; // Here, the division happens
even when b is 0…
#include <stdio.h>
int main() {
int roomlen, roomwid;
int desklen, deskwid;
printf("Enter the length and width of the room.\n");
scanf("%d%d",&roomlen, &roomwid);
printf("Enter the length and width of the desk.\n");
scanf("%d%d",&desklen, &deskwid);
if ((deskwid <= roomwid) && (desklen <= roomlen))
printf(“The desk will fit in the room.\n”);
else
printf(“The desk will not fit in the room.\n”);
return 0;
}
Revision #1
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//Adjust lengths and widths, if necessary
if (roomlen < roomwid) {
roomlen = roomwid;
roomwid = roomlen;
}
if (desklen < deskwid) {
desklen = deskwid;
deskwid = desklen;
}
• What’s WRONG with this solution?
Corrected Program
• Add the following after the scanfs to the original
program:
– //Adjust lengths and widths, if necessary
–
if (roomlen < roomwid) {
–
temp = roomlen;
–
roomlen = roomwid;
–
roomwid = temp;
–
}
–
if (desklen < deskwid) {
–
temp = desklen;
–
desklen = deskwid;
–
deskwid = temp;
–
}
Another Solution
• if ((deskwid <= roomwid) && (desklen <= roomlen))
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printf(“The desk will fit in the room.\n”);
• else if ((deskwid<=roomlen) && (desklen<=roomwid))
•
printf(“The desk will fit in the room.\n”);
• else
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printf(“The desk will not fit in the room.\n”);