expression isys 350. performing calculations basic calculations such as arithmetic calculation can...
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Expression
ISYS 350
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Performing Calculations• Basic calculations such as arithmetic calculation can be
performed by math operatorsOperator Name of the operator Description
+ Addition Adds two numbers
- Subtraction Subtracts one number from another
* Multiplication Multiplies one number by another
/ Division Divides one number by another and gives the quotient
% Modulus Divides one number by another and gives the remainder
Other calculations: Use Math class’s methods.Example: Math.Pow(x, y)
double x = 3.0, y = 2.0, z;z=Math.Pow(x,y);
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Order of Evaluation
• Operator Multiples• 1 ( ) Inner to outer, left to right• 2. Power left to right• 3. *, / left to right• 4. +, - left to right
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Formula to Expression
CD
BA
DC
ABCD
BA
ABAAB
22
DC
AB
CD
BA
B
A
X
X
Y
X
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Increment/Decrement Operators
++ Increment Adds 1 to the operand (x = x + 1).
-- Decrement Subtracts 1 from the operand (x = x - 1).
int x = 14;int y = 8;Int z = 10;int result7 = --y; // result7 = 7int result8 = ++x; // result8 = 15, x = 15++z; // z= 11
double a = 8.5;double b = 3.4;double result15 = --a; // result15 = 7.5double result16 = ++b; // result16 = 4.4
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Compound (Shortcut) Operators
Operator
+= Adding the operand to the starting value of the variable.-= Subtracting the operand from the starting value of the variable.
*= Multiplying the operand by the starting value of the variable./= Dividing the operand by the starting value of the variable.%= Remainder after dividing the right operand by the value in the variable.
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Statements that use the same variable on both sides of the equals sign
count = count + 1; // count is increased by 1 count = count – 1; // count is decreased by 1 total = total + 100.0; // total is increased by 100.0 total = total – 100.0; // total is decreased by 100 price = price * .8; // price is multiplied by 8 sum = sum + nextNumber; // sum is increased by value of nextNumber
Statements that use the shortcut operators to get the same results
count += 1; // count is increased by 1 count -= 1; // count is decreased by 1 total += 100.0; // total is increased by 100.0 total -= 100.0; // total is decreased by 100.0 price *= .8; // price is multipled by 8 sum += nextNumber; // sum is increased by the value of nextNumber
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Decrement/Increment by 1
private void button1_Click(object sender, EventArgs e) { int myInt; myInt = int.Parse(textBox1.Text); // myInt-=1; // myInt = --myInt; --myInt; textBox1.Text = myInt.ToString(); } private void button2_Click(object sender, EventArgs e) { int myInt; myInt = int.Parse(textBox1.Text); //myInt += 1; //myInt = ++myInt; ++myInt; textBox1.Text = myInt.ToString(); }
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Decrement/Increment by any Step Value
private void button1_Click(object sender, EventArgs e) { int stepValue; stepValue = int.Parse(textBox2.Text); int myInt; myInt = int.Parse(textBox1.Text); myInt -= stepValue; // myInt = myInt - stepValue; textBox1.Text = myInt.ToString(); } private void button2_Click(object sender, EventArgs e) { int stepValue; stepValue = int.Parse(textBox2.Text); int myInt; myInt = int.Parse(textBox1.Text); myInt += stepValue; // myInt = myInt + stepValue; textBox1.Text = myInt.ToString(); }
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Prefix/Postfix Increment/Decrement Operators
int a = 5;int b = 5;int y = ++a; // a = 6, y = 6int z = b++; // b = 6, z = 5
•When you use an increment or decrement operator as a prefix to a variable, the variable is incremented or decremented and then the result is assigned. •When you use an increment or decrement operator as a postfix to a variable, the result is assigned and then the variable is incremented or decremented.
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Counter• Example: Keep track the number of times a
user clicks a button• Need to declare a variable:
int Counter=0;
• Need to increase the counter by 1 when the button is clicked:
Counter = Counter + 1; // Or
Counter+=1; // Or
++Counter;
Question: Where to declare this variable?
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Example
int Counter = 0;private void button1_Click(object sender, EventArgs e) { Counter = Counter + 1; textBox1.Text = Counter.ToString(); }
private void button1_Click(object sender, EventArgs e) { int Counter = 0; Counter = Counter + 1; textBox1.Text = Counter.ToString(); }
Incorrect:
Correct:
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Variable Scope• The scope of a variable determines its
visibility to the rest of a program.– Procedural-level scope: declared in a procedure
and visible only in the procedure.– Class-level scope: declared in a class but outside
any procedure; visible to all procedures in the class.