Lesson7 incdecoperators
- 1. Lesson 7: Autoincrement and Autodecrement Operators in C++ Discussion 1. C++ uses autoincrement and autodecrement operators, such that if we have a variable count, count++; would add 1 to count in the same way that the assignment statement count = count + 1; does, and count-- would subtract 1 from count, in the same way that count = count -1; does. 2. Recall that count = count + 1 may also be expressed as count += 1. 3. Recall that count = count - 1 may also be expressed as count -= 1. 4. In C++, we are allowed to express count +=1 as count++. 5. In C++, we are allowed to express count -=1 as count--. 6. Looks simple enough. However, there is another expression that looks very similar, and that can add or subtract 1 to a variable: ++count and --count. 7.Needless to say, we can only do this to integer variables, and not only to the variable count, but to other variables as well, so we can have vote++, --candy, and the like. 8. Moreover, we can only apply the increment and decrement operators to single variables. Expressions like (count+i)++ , or -–(x+y) are not allowed in C++. 9. When the operator is placed before the variable, say, ++count, the operator ++ is in prefix form; putting it as count++ renders it in postfix form. 10. What's the difference? Let's consider putting the expression in an assignment statement. Recall that the expression, say count++, is actually an assignment statement in itself, so that you we shall be doing more than one assignment in the statements below: m= 1; j = 2 * m++; 11. In this postfix form, the following things happen: 1. The old/current value of m, which is 1, is multiplied by 2 2. The old/current value of m is incremented by 1 (which means that new value of 2 is assigned to m) 3. The result of multiplication is stored or assigned to j. Take note that there were two assignment operations done: one on m andthe other on j. 12. If we have the following statements instead: m= 1; j = 2 * ++m; the following steps would be executed: 1. The old/current value of m which is 1 is incremented, making it 2 (The first assignment) 2. This new value of m is multiplied by 2 3. The product of the multiplication is stored or assigned to j.(Second assignment) Sample Programs: 1. incDecPost.cpp 2. incDecPre.cpp Exercise: 1. Try the sample program incDec.cpp given in incDecSourceFile.pdf and study the operations done by the prefix and postfix increment and decrement operators. 2. What happens if you remove line#26? Explain the output when this line is removed. Submit your explanation in pdf format with filename incDecfLastname. 3. Create a program that will output two columns, with headings “Text”, and “Numeral”, for numbers 1 through 5. File name is tabLastname.cpp. Sample output is shown below. Text Numeral One 1 Two 2 : : TSPaccarangan Increment and Decrement Operators September 14, 2009