printf("this program adds the value 10 to a given integer number.\n\n");

Transcription

1 PA1 Sample Solution Program 1 void add10(int *n); //Prototype int n; printf("this program adds the value 10 to a given integer number.\n\n"); printf("please enter an integer number: "); scanf("%d", &n); add10(&n); //Calls the function to add 10. Gives the address of n as parameter. printf("\nthe result is %d \n\n", n); void add10(int *nptr) // initializes pointer nptr with the address of n. MOV EAX, nptr // copy the contents of the pointer to EAX MOV EDX, [EAX] // copy the contents of the data segment memory location //addressed by EAX into EDX ADD EDX, 10 // adds 10 to the contents of EDX MOV [EAX], EDX // copy the contents of EDX into the data segment memory //location addressed by EAX Program 2 ; ; void swapelements(char *tableptr, int n); char table[52]; // Defines an array of 52 elements. int n, i, done; table[0] = 'A'; //Fills the array with the letters A-Z and a-z. for (i = 1; i < 52; i++)

2 if (i < 26 i > 26) table[i] = table[i-1] + 1; else if (i == 26) table[i] = 'a'; done = 0; while(done == 0) printf("please enter a number between 0 and 52: "); scanf("%d", &n); if (n < 0 n > 52) done = 1; else if (n == 0) for (i = 0; i < 52; i++) printf("%c ", table[i]); printf("\n"); else swapelements(table, n); void swapelements(char *table, int n) MOV EBX, table // copies the start address of table in EBX DEC n // Decrement n by 1 MOV EDI, n // copies the value of n into EDI MOV AL, [EBX] // copies the contents of position table[0] into AL MOV AH, [EBX + EDI] // copies the contents of position table[0+n] into AH MOV [EBX], AH // copies the contents of AH into the contents //addressed by EBX (table[0]) MOV [EBX + EDI], AL // copies the contents of AL into the contents //addressed by EBX+EDI (table[0+n)

3 Program 3 void initializetable(char *table); char table[26]; // Defines an array of 26 elements. int i; initializetable(table); // calls the function with the address of table given as //parameter printf("the table contents are: "); // Prints the contents of the table for (i = 0; i < 26; i++) printf("%c ", table[i]); printf("\n"); void initializetable(char *table) // Initializes a pointer with the address of table MOV EBX, table // Copies the starting address of table into EBX MOV AL, 61H // Loads the ASCII code for the letter 'a' into AL MOV EDI, 0 // Loads EDI with the value 0 (for getting the //element of the array) MOV ECX, 26 // Loads the counter ECX with the value 26 (number //of iterations) START: // Define label MOV [EBX+EDI], AL // Copies the contents of AL to the data addressed //by EBX + EDI ADD AL, 01H // Adds 1 to AL to change the ASCII code for the //next letter ADD EDI, 1 // Adds 1 to EDI to be ready to address the next //element in the array LOOP START // Repeats the code from the label START and //decrements the counter ECX // by 1 until it reaches 0 and the loop exits.

4 Program 4 void reverse(char *c1, char *c2, char *c3, char *c4); // prototype of the function char c1, c2, c3, c4; //Recieves the 4 characters from the user printf("enter the four characters and then press ENTER: "); scanf("%c", &c1); scanf("%c", &c2); scanf("%c", &c3); scanf("%c", &c4); //Calls the function with the characters addresses as parameters reverse(&c1, &c2, &c3, &c4); // Prints the characters printf("\nthe characters in reverse are: %c %c %c %c\n\n", c1, c2, c3, c4); /* Reverses the order of the characters. Initializes four pointers to the character addresses.*/ void reverse(char *c1, char *c2, char *c3, char *c4) PUSH c1 // Stores the address of c1 in the stack PUSH c2 // Stores the address of c2 in the stack PUSH c3 // Stores the address of c3 in the stack PUSH c4 // Stores the address of c4 in the stack POP EDX // Gets the address of c4 from the stack and stores it in EDX POP ECX // Gets the address of c3 from the stack and stores it in ECX POP EBX // Gets the address of c2 from the stack and stores it in EBX POP EAX // Gets the address of c1 from the stack and stores it in EAX PUSH [EAX] // Stores the contents at the address of EAX in the stack PUSH [EBX] // Stores the contents at the address of EBX in the stack PUSH [ECX] // Stores the contents at the address of ECX in the stack PUSH [EDX] // Stores the contents at the address of EDX in the stack POP [EAX] //Last data in the stack and stores it in the address of EAX POP AX // Move the stack pointer two bytes up (SP + 2) POP [EBX] // Last data in the stack and stores it in the address of EBX POP [ECX] // Last data in the stack and stores it in the address of ECX POP [EDX] // Last data in the stack and stores it in the address of EAX

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