C++ Basics

Prof. Shermane Austin

Learning Programming Language Basics

• Data Types – simple • Expressions• Relational and Logical Operators• Conditional Statements• Arrays• Iteration• Memory Allocation• I/O• Functions

Hello World

//Simple C++ program#include <iostream> //input and output library#include <string> //string libraryusing namespace std; // predefined objectsint main() //first function, { //function delimiter

cout << “Hello world!” << endl; //output stream return 0; //ends execution and returns]

Simple Data Types

• Int – 32 bit, optional qualifiers: long, short

• Float – 32 bit, IEEE floating point

• Double – 64 bit, optional qualifer: long

• Char – 8 bit

• Byte – 8 bit

Operators

• Arithmetic– +, -, /, * – % - modulus or remainder, integer only, e.g. 23%4

• Relational – <, >, <=, >=, !=, ==– (c == a) \\ common error is omitting one of the =– Be careful using != or == with floating point values,

rounding occurs at the machine level• Logical

– And &&, e.g. (c <= a) && (c >= b)– Or ||, e.g. (c <= a) || (c >= b)

Operator shortcuts – Compound Assignment

• Increment, Decrement++, --a = a + 1; \\can be written as a++;a++, ++a, a--, --aPosition of operator is important, e.g.b = f(a++); \\a is incremented after f(a) callc = f(++a); \\a is incremented before f(a) call• Compound Assignment Operatorsint a;…a = a + 5;a += 5;Can be used with all arithmetic operators

Exercise - 1

• Compute volume of an object• Read in:

– Object mass (grams)– Object density (grams per cubic centimeter)

• Output:Volume (cubic centimeters)

• Relationship:Density = Mass/Volume

Code Needs

• Determine variables (with types needed)

• Issue prompts – use cout, e.g.

Cout << “Object Mass?” << endl;

• Read in values – use cin, e.g.

Cin >> mass;

• Compute Distance and Velocity

Conditional Expressions

• Any combination of logical and relational operators

• Use () as needed• Examples:Simple if statement if( a < b) s1 else s2

If/else statement

• General format – single statement execution on true condition

• Long format – multiple statement execution on true condition

• General rule: more than one statement under if and/or else condition requires {}

• Short-hand format – single statement

• Nested if statements

If – single statement

Format:

if(expression)

s1;

else

s2;

If – multiple statementsFormat:

if(expression){

s1; s2; …

}else{

s1; s2; …

}

If shorthand

• Used only with single statements• Format:Expression ? S1 : s2;Example: c != b ? c++ : b++;Example: int a,b; … int min = a <= b ? a : b ;

Short-circuit evaluation

• && - evaluation terminates with first false condition

• || - evaluation terminates with first true condition

• Done to insure objects can be properly manipulated, e.g.– (i != 0) && ((j/i) > 5)

Arrays

• Included in C++ for backward compatibility with C

• Arrays less popular and class representation of lists, especially the vector class more frequently used

• Vector class is an example of container classes is defined in the Standard Template Library (STL)

Simple arrays - Declaration

const int N = 20;const int M = 40;const int MaxListSize = 1000;// Note: const qualifier used to denote constant

values//Declaration examples:int a[10];float c[M*N];int Values[MaxListSize];

Simple Arrays - Referencing

• Array elements are referenced using subscripts or indices

• First index in C++ is 0• Examples: a[0] = b; a[i++] = a[j] + 3; a[a[k]] = 12;• Warning: No automatic checking for array

boundaries. Illegal subscripts will result in inaccurate memory references or storage

Simple Array - Initialization

• Int frequency[5] = {0,0,0,0,0};

• Int total[5] = {0}; // first element set to 0, remainder are uninitialized and default at 0

• Int digits[] = {0,1,2,3,4,5,6,7,8,9};

• Int zero[] = {0}; //one-element array

Iteration

• For-loops

• While-loops

Iteration using while

• Format: while (conditional expression){

s1; …}Statement in the block are executed as long as

condition is trueIf condition is evaluated to false, statements are

never executed

Interation using for

• Format:

for (ForInit ; ForExpression; PostExpression)

{

}

ForInit – initialization step to start loop

ForExpression – logical expression

PostExpression – next iteration of loop

For examples

for( i = 0; i<= maxsize; i++){}for(j=minsize; j < maxsize; j+=2){}for(k = maxsize; k > minsize; k--){}

Exercises

• Compute n! using a for loop

• Compute the nth Fibonacci term using a while loop

• Example, compute roots of a quadratic equation://Quadratic roots#include <iostream>#include <string>#include <math.h>Using namespace std;int main(){

double a, b, c; cout << “Coefficients for quadratic equation: “; cin >> a >> b >> c; if ((a != 0) && ((b*b – 4*a*c) > 0)) { double radical = sqrt(b*b – 4 * a * c); double root1 = (-b + radical) / (2 * a); double root2 = (-b – radical) / (2 * a); cout << “ roots are “ << root1 << “ and “ << root2 << endl; } else { cout << “ No real roots “ << endl; } return 0;}

Compute area of a circle#include <iostream>#include <string>Using namespace std;const float Pi = 3.1415int main(){ float radius; cout << “Enter radius: ”; cin >> radius; //compute area float area = Pi * radius * radius; //output cout << “Area = “ << area;}

More general using functions#include <iostream>#include <string>Using namespace std;float CircleArea(float r){ const float Pi = 3.1415; return Pi * r * r;}int main(){ float radius; cout << “Enter radius: ”; cin >> radius; //compute area float area = CircleArea(radius); //output cout << “Area = “ << area;}

Function prototyping

• Functions cannot be used until they are defined

• Can create problems with functions calling other functions

• Use prototype conventions

• Define function prototype before main

• Implement function after main

Prototype Example#include <iostream>#include <string>Using namespace std;float CircleArea(float r);int main(){ float radius; cout << “Enter radius: ”; cin >> radius; //compute area float area = CircleArea(radius); //output cout << “Area = “ << area;}float CircleArea(float r){ const float Pi = 3.1415; return Pi * r * r;}

Homework

• Write a program for integrating a quadratic polynomial

• User input will be– Quadratic coefficients: a1, a2, a3– Interval of interest : n1, n2

• Output will be the area