1 CS161 Introduction to Computer Science Topic #4

CS161 Topic #42 Today in CS161 Assignments/Questions –What is needed for Program #2? –Using the Math Library –Input/Output and Formatting –Sample Algorithm

CS161 Topic #43 To Raise to Power of... In C++ there is no operator that will raise some number by another For example, for x 3 you can’t type: –x**3ILLEGAL! Instead, you must use the pow function float answer; answer = pow(x, 3);

CS161 Topic #44 To Raise to Power of... To use the power function, we must do two very important things... –include the math library: #include –compile our programs using a -lm flag g++ -lm prog2.cpp

CS161 Topic #45 Next, to Format our Output We must learn about precision By default, real numbers are displayed with no more than 6 digits, plus the decimal point This means that 6 significant digits are displayed in addition to the decimal point and a sign if the number is negative

CS161 Topic #46 Default Precision -- Examples float test; cout << “Please enter a real number”; cin >> test; cout << test; InputResulting Output

CS161 Topic #47 To Change Precision float test; cout << “Please enter a real number”; cout.precision(3);//3 instead of 6!! cin >> test;cout << test << endl; InputResulting Output e+04 (Exponential notation)

CS161 Topic #48 Another way to do this... #include float test; cout << “Please enter a real number”; cin >> test; cout <<setprecision(3) << test << endl; setprecision is a manipulator To use it, we must include the iomanip.h header file There is no difference between cout.precision(3)andcout <<setprecision(3)

CS161 Topic #49 What is “width”? The width of a field can be set with: cout.width(size); If what you are displaying cannot fit, a larger width is used –to prevent the loss of information Important –Width is only in effect for the next output

CS161 Topic #410 How does width work... float test; cout.precision(4);cout.width(10); cin >>test;cout << test; cout <<endl <<test; InputResulting Output

CS161 Topic #411 Another way to do this... #include float test; cout.precision(4); cin >>test; cout <<setw(10) << test; cout <<endl <<test; InputResulting Output

CS161 Topic #412 Trailing Zeros For real numbers, trailing zeros are discarded when displayed To display trailing zeros we use: cout.setf(ios::showpoint); InputResulting Output (for an precision of 3 or greater)

CS161 Topic #413 Displaying Trailing Zeros float test; cout.precision(4); cout.setf(ios::showpoint); cin >>test;cout << test <<endl; cout.unsetf(ios::showpoint); //reset... cout <<test; InputResulting Output

CS161 Topic #414 Displaying Dollars and Cents! There is another meaning to precision... –if we put in our programs: cout.setf(ios::fixed,ios::floatfield); –then, subsequent precision applies to the number of digits after the decimal point! cout.precision(2);cout <<test; To display trailing zeros we use: cout.setf(ios::showpoint); InputResulting Output

CS161 Topic #415 Displaying Dollars and Cents! Since we ALSO want trailing zero displayed...do all three: cout.setf(ios::fixed,ios::floatfield); cout.precision(2); cout.setf(ios::showpoint); cout <<test; To display trailing zeros we use: cout.setf(ios::showpoint); InputResulting Output

CS161 Topic #416 Now... the Algorithm... Your algorithm is not: –I sat down at the terminal –I got into the editor –I entered my program –I tried to compile it but got errors I DON”T WANT TO SEE THIS!!!!

CS161 Topic #417 Your Algorithm... First define the major tasks Then break down these into subtasks For example, the major tasks might be: –Welcome the user –Get the loan amount, interest rate, duration –Calculate the monthly payment –Display the results –Sign off Message Not Detailed Enough! But...a good start...