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Today’s Lecture

Today’s Lecture. Predefined Functions. Introduction to Functions. Reuse Issue Building Blocks of Programs Two types of functions Predefined Programmer defined. Predefined Functions. Predefined in the libraries Example: Calculate the square root of a number

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Today’s Lecture

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  1. Today’s Lecture Predefined Functions

  2. Introduction to Functions • Reuse Issue • Building Blocks of Programs • Two types of functions • Predefined • Programmer defined

  3. Predefined Functions • Predefined in the libraries • Example: • Calculate the square root of a number • double sqrt(double) is defined in library <cmath> • Three parts: • Return type • Function name • Argument list

  4. The Function Call • To use: • Must "#include" the library that defines the function <cmath> • Provide required arguments • Example: double root; root = sqrt (9.0); • The argument in a function call (9.0) can be a literal, a variable, or an expression

  5. A Larger Example: Display 3.1 A Predefined Function That Returns a Value (1 of 2)

  6. A Larger Example: Display 3.1 A Predefined Function That Returns a Value (2 of 2)

  7. Predefined Functions • Libraries full of functions for our use! • Two types: • Those that return a value • Those that do not (void) • Must "#include" appropriate library • e.g., • <cmath>, <cstdlib> (Original "C" libraries) • <iostream> (for cout, cin)

  8. More Predefined Functions • #include <cstdlib> • abs() // Returns absolute value of an int • pow(x, y) • Returns x to the power y • Notice this function receives two arguments • A function can have any number of arguments, of varying data types

  9. Even More Math Functions: Display 3.2 Some Predefined Functions (1 of 2)

  10. Even More Math Functions: Display 3.2 Some Predefined Functions (2 of 2)

  11. Predefined Void Functions • No returned value • Performs an action, but sends no "answer" • All aspects same as functions that "return a value" • They just don’t return a value! • Example • exit(int)

  12. Random Number Generator • Return "randomly chosen" number • Used for simulations, games • rand() • Takes no arguments • Returns value between 0 & RAND_MAX • Scaling • Squeezes random number into smaller range rand() % 6 • Returns random value between 0 & 5 • Shiftingrand() % 6 + 1 • Shifts range between 1 & 6 (e.g., die roll)

  13. Random Examples • Random double between 0.0 & 1.0:rand()/(double)(RAND_MAX) • Type cast used to force double-precision division • Random int between 1 & 6:rand() % 6 + 1 • "%" is modulus operator (remainder) • Random int between 10 & 20:rand() % 10 + 10

  14. Pseudorandom Numbers • The function rand() takes no arguments and returns a integer in the rage of [0, RAND_MAX] • Numbers appears to be random, but really not. • It is called pseudorandom numbers • The sequence of the random is determined by seed

  15. Pseudorandom Numbers • If you start rand with the same seed, you will produce the same sequence random number • To get true random number, use function srand to reset seed. void srand(int)

  16. Character Functions • Include <cctype> bool isdigit(char) bool isalpha(cha) bool isspace(char) bool islower(char) bool isupper(char) int tolower(char) int toupper(char)

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