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EEE 243B Applied Computer Programming

EEE 243B Applied Computer Programming. Pointers and arrays practice. Practice. Write an include instruction that has stddef.h in it Declare a function prototype named IntArray that returns a pointer to int and that takes three pointers to int as parameters (px,py and pz)

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EEE 243B Applied Computer Programming

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  1. EEE 243BApplied Computer Programming Pointers and arrays practice

  2. Practice • Write an include instruction that has stddef.h in it • Declare a function prototype named IntArray that returns a pointer to int and that takes three pointers to int as parameters (px,py and pz) • Start a main() function returning void and having no parameters Maj JGA Beaulieu & Capt MWP LeSauvage

  3. Practice #include <stddef.h> int *IntArray(int *px, int *py, int *pz); void main(void) { }//main Maj JGA Beaulieu & Capt MWP LeSauvage

  4. Practice • Inside the main function: • Declare two integers, named firstInt (value of 5) and secondInt (value of 10) • Declare a pointer to int named pInt (initialize all pointers to NULL) • Declare a pointer to pointer to int named ppInt • Declare an array of int size 2 named numbers • Initialize this array to all zeros Maj JGA Beaulieu & Capt MWP LeSauvage

  5. Practice #include <stddef.h> int *IntArray(int *px, int *py, int *pz); void main(void) { int firstInt = 5; int secondInt = 10; int *pInt = NULL; int **ppInt = NULL; int numbers[2] = {0,0}; } //main Maj JGA Beaulieu & Capt MWP LeSauvage

  6. Practice • Inside the main function: • Call the function IntArray in your code so that the return value of the function is put into the pointer variable pInt • Pass the parameters to IntArray in the following order: • Address of firstInt, address of secondInt and address of the numbers array • Make ppInt point to pInt Maj JGA Beaulieu & Capt MWP LeSauvage

  7. Practice #include <stddef.h> int *IntArray(int *px, int *py, int *pz); void main(void) { int firstInt = 5; int secondInt = 10; int *pInt = NULL; int **ppInt = NULL; int numbers[2] = {0,0}; pInt = IntArray(&firstInt,&secondInt,numbers); ppInt = &pInt; } //main Maj JGA Beaulieu & Capt MWP LeSauvage

  8. Practice • Define the IntArray function to do the following: • Declare a pointer to int,pInt and make it point to the third parameter in the list (the array) • Put the first integer in the first element of the array • Post increment your pointer • Put the second parameter in the second element of the array • Return the address of the array (remember where you are pointing after the post increment) Maj JGA Beaulieu & Capt MWP LeSauvage

  9. Practice int *IntArray(int *px, int *py, int *pz) { int *pInt = pz; //pz is an address *pInt++ = *px; //note ++ is higher priority than * *pInt-- = *py; //pInt was pointing to numbers[1] return pInt; //Now pInt points to numbers[0] } //IntArray Maj JGA Beaulieu & Capt MWP LeSauvage

  10. #include <stddef.h> int *IntArray(int *px, int *py, int *pz); void main(void) { int firstInt = 5; int secondInt = 10; int *pInt = NULL; int **ppInt = NULL; int numbers[2] = {0,0}; printf("Value of first int in array: %d\n",numbers[0]); //print initial values printf("Value of second int in array: %d\n",numbers[1]); pInt = IntArray(&firstInt,&secondInt,numbers); //function call ppInt = &pInt; printf("Value of first int in array: %d\n",numbers[0]); //print value with index printf("Value of second int in array: %d\n",numbers[1]); printf("Value of first int in array: %d\n",*pInt++); //print with pointer printf("Value of second int in array: %d",**ppInt); //print with p-to-r to int getchar(); //wait } //main int *IntArray(int *px, int *py, int *pz) { int *pInt = pz; //pz is an address *pInt++ = *px; //note ++ is higher priority than * *pInt-- = *py; //pInt was pointing to numbers[1] return pInt; } //IntArray

  11. Practice • Soon we will be using the command line arguments capabilities of C • Remember that main() is a function like any other function • It is this function that is the root of your program • When you declare your main() function you normally do the following: void main (int argc, char **argv) Maj JGA Beaulieu & Capt MWP LeSauvage

  12. Practice • Remember that you can access the command line arguments (argv) one at a time using the array notation: argv[0], argv[1], … argv[argc -1] • argc is the count of the number of elements in the array • argv[0] is the name of the program Maj JGA Beaulieu & Capt MWP LeSauvage

  13. Practice • You are experienced with the dll.exe program used to download your programs into the Roverbot. • Write a main() function for dll.c so that you can separate the tockens from the command line • You are to recognize the following two options –t with value usb and –r [0..15] • If the command line argument for –t option is not usb or that –r is not in the range, an error must be generated Maj JGA Beaulieu & Capt MWP LeSauvage

  14. Practice • Include stdio.h, stdlib.h and string.h in your header • You will be using the atoi function that can convert alphanumeric characters to ints: int atoi(const char *real_num); • You will also be using strcmp to compare the tockens you extract with constants in your code: int strcmp(const char *str1, const char *str2); • Define your main() Maj JGA Beaulieu & Capt MWP LeSauvage

  15. Practice #include <stdlib.h> #include <string.h> #include <stdio.h> void main(int argc, char **argv) { }//main Maj JGA Beaulieu & Capt MWP LeSauvage

  16. Practice • Declare two int variables, one to count the number of arguments (numArgs) and the other to store the Roverbot number (bot) if the –r option is selected • Write an if statement that verifies that you have more than 2 arguments (argc) • If not, print an error message (printf) and exit (exit(1)) • Write a loop that iterates through the arguments (tokens) Maj JGA Beaulieu & Capt MWP LeSauvage

  17. Practice #include <stdlib.h> #include <string.h> #include <stdio.h> void main(int argc, char **argv) { int numArgs = 1; int bot = 0; if (argc <= 2) { printf("Need more arguments"); exit(1); } while (numArgs < argc) { }//while } Maj JGA Beaulieu & Capt MWP LeSauvage

  18. Practice • A parser, like the dll.exe program, iterates through the command line arguments (**argv) and checks for the validity of options and their values • Write your first token parsing statement: • With the if statement, check to see if the command line argument (argv[numArgs]) is the –t option • For this you will need the strcmp() function • If it is, check if the next token is the usb value • If it is, then print some statement to this effect • If it is not then get out with an error message about the value of the tty not being valid Maj JGA Beaulieu & Capt MWP LeSauvage

  19. Practice … while (numArgs < argc) { if (!strcmp(argv[numArgs],"-t")) { //get the kind of tty numArgs++; if (!strcmp(argv[numArgs],"usb")) printf("We have -t and usb\n"); else { printf("ERROR - Invalid tty"); exit(1); }//else }//if -t }//while … Maj JGA Beaulieu & Capt MWP LeSauvage

  20. Practice • Write your second token parsing statement: • With the else-if statement, check to see if the next command line argument (argv[numArgs]) is the –r option • If it is, check if the valueof the next token is within 0..15 range. • You will need the atoi()function to transform the string into int • If the value is good, then print some statement to this effect • If it is not then get out with an error message stating that the value of the bot was not in range Maj JGA Beaulieu & Capt MWP LeSauvage

  21. Practice … else if (!strcmp(argv[numArgs],"-r")) { numArgs++; bot = atoi(argv[numArgs]); if (bot >= 0 && bot <= 15) printf("We have -r with bot# %d\n", bot); else { printf("ERROR - Invalid bot number"); exit(1); } }//if -r … Maj JGA Beaulieu & Capt MWP LeSauvage

  22. Practice • If the token does not match any of the options that you want, give an error message (not –t or –r) • Do not forget to update your condition (numArgs) close your loop • Voila!! Your first parser Maj JGA Beaulieu & Capt MWP LeSauvage

  23. Practice }//if -r else { printf("ERROR - Invalid argument"); exit(1); }//invalid arg numArgs++; }//while exit(0); }//main Maj JGA Beaulieu & Capt MWP LeSauvage

  24. #include <stdlib.h> #include <string.h> #include <stdio.h> void main(int argc, char **argv) { int numArgs = 1; int bot = 0; if (argc <= 2) { printf("Need more arguments"); exit(1); } while (numArgs < argc) { if (!strcmp(argv[numArgs],"-t")) { //get the kind of tty numArgs++; if (!strcmp(argv[numArgs],"usb")) printf("We have -t and usb\n"); else { printf("ERROR - Invalid tty"); exit(1); }//else }//if -t else if (!strcmp(argv[numArgs],"-r")) { numArgs++; bot = atoi(argv[numArgs]); if (bot >= 0 && bot <= 15) printf("We have -r with bot# %d\n", bot); else { printf("ERROR - Invalid bot number"); exit(1); } }//if -r else { printf("ERROR - Invalid argument"); exit(1); }//invalid arg numArgs++; }//while exit(0); }//main

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