Working with numbers
Academic year 2011/12Objectives:
- Basic method to obtain input data
- Use arithmetic, assignment, comparison and logic operators
Basic method to obtain input
There are detailed formatting rules to specify the data type when obtaining input and displaying output:
- Obtaining input
- List of input formats by data type
- General syntax of formatted input formats
- Formatted input functions for all data types (including the scanf() function)
- Displaying output
- List of output formats by data type
- General syntax of formatted output formats
- Formatted output functions for all data types (including the printf() function)
An expression is a combination of operators and operands
- Unary operators require only 1 operand, e.g. line 6 below.
- Binary operators require 2 operands, e.g. line 9 below.
- There is only one ternary operator in the C language, which is the conditional operator ? : that requires 3 operands, e.g. line 12 below.
Automatic data type conversion
The C compiler automatically converts the value on the right side of an assignment operation to match the data type of the variable on the left side.
Arithmetic operators
| Operator | Example | Meaning |
| * | x * y | Multiply x and y |
| / | x / y | Divide x by y |
| % | x % y | The remainder after dividing x by y |
| + | x + y | Add x and y |
| - | x - y | Subtract y from x |
| + | +x | Value of x |
| - | -x | Arithmetic negative of x |
| ++ | ++x | Increase x by 1 before using x |
| -- | --x | Decrease x by 1 before using x |
| ++ | x++ | Increase x by 1 after using x |
| -- | x-- | Decrease x by 1 after using x |
Use arithmetic operators to perform the tasks below:
- Count 1 to 10
- Count 10 to 1
- Count odd numbers 1 to 10
- Count multiples of 5 from 100 to 50
Evaluation trees show order of precedence
Operators in C arithmetic expressions follow the same order of precedence as normal math expressions.
- Parentheses are the highest precedence
- Unary operators, such as ++ or --
- Positive and negative sign operators, e.g. + or -
- Multiplication and division operators
- Addition and subtraction operators
- Assignment operators are the lowest precedence, such as = or *=
Parentheses can make programs easier to read
Like math expressions, parentheses can be used to indicate specific orders of precedence. The use of extra parentheses in a complex arithmetic expression can make it easier to read and change later.
Division depends on the data type of the operands
The result of division using all integer operands is an integer value. If a fractional result is required, then one of the operands must be forced to be float or double type.
Assignment operators
| Operator | Example | Meaning |
| = | x = y | Assign the value of y to the variable x |
| *= | x *= y | Assign the product of x multiplied by y to the variable x |
| /= | x /= y | Assign the quotient of x divided by y to the variable x |
| += | x += y | Assign the sum of x and y to the variable x |
| -= | x -= y | Assign the result of subtracting y from x to the variable x |
When using the combination assignment operators, e.g. *=, the expression on the right side of the operator is fully evaluated before the assignment operator is applied.
Comparison operators only have 2 possible values
- Value 1 to mean logical true
- Value 0 to mean logical false
| Operator | Example | Meaning |
| < | x < y | 1 if x is less than y |
| <= | x <= y | 1 if x is less than or equal to y |
| > | x > y | 1 if x is greater than y |
| >= | x >= y | 1 if x is greater than or equal to y |
| == | x == y | 1 if x is equal to y |
| != | x != y | 1 if x is not equal to y |
Be careful using equal signs
Errors often happen with the use of the equal signs:
- One equal sign, = , is the assignment operator
- Two consecutive equal signs, == , is the equality comparison operator
Logic operators only have 2 possible values
- Non-zero value to mean logical true
- 0 value to mean logical false
| Operator | Example | Meaning |
| && | x && y | 1 if the values of x and y are both not 0 |
| || | x || y | 1 if the values of x or y are not 0 |
| ! | !x | 1 if the value of x is equal to zero. |
Review questions
Working with numbers
In the C program below, what should replace the XXX placeholder at line 7?
- #include <stdio.h>
- int main( void )
- {
- int age;
- scanf( "%d", XXX );
- age += 3;
- }
Review questions
Working with numbers
In the C program below, how could you replace the unary operator with a binary operator?
- #include <stdio.h>
- int main( void )
- {
- int age;
- scanf( "%d", &age );
- age += 3;
- }
Review questions
Working with numbers
In the C program below, what is the displayed output?
- #include <stdio.h>
- int main( void )
- {
- int age;
- scanf( "%d", &age );
- age += 3;
- }
Review questions
Working with numbers
In the C program below, how could you change the comparison operator so that the displayed output would be 1?
- #include <stdio.h>
- int main( void )
- {
- int age;
- scanf( "%d", &age );
- age += 3;
- }