102
Lab ECS 8
October 19/20, 2004
Anywhere that I ask you to observe what happens, write down your observations in the space provided.
"'I wonder if I've been changed in the night? Let me think: was I the same when I got up this morning? I almost think I can remember feeling a little different. But if I'm not the same, the next question is 'Who in the world am I?' Ah, that's the great puzzle!'" - Alice in Wonderland by Lewis Caroll
I. Enter this program: /* lab8.c */ #include<stdio.h> #include<math.h> /*for fabs */ /*function prototypes*/ void printparts( double num ); int main(void) { double a=5.3, b=-87.34, c=0; printf("%f\n", a); printparts( a); printf("\n%f\n", b); printparts(b); printf("\n%f\n",c); printparts(c); return(0); } /* Separates a number into three parts: a sign ( +, -, or blank) a whole number magnitude a fractional part magnitude Example: -4.25 has sign - , whole number magnitude 4, fractional part magnitude .25 This function prints the three parts on three separate lines. */ /*********printparts**************/ void printparts( double num ) { char sign; int whole; double frac;
double magnitude; /*local variable - magnitude of num*/ /* Determine sign of num */ if (num < 0) sign = '-'; else if (num == 0) sign = ' '; else sign = '+'; /* Finds magnitude of num and separates it into whole and fractional parts. */ magnitude = fabs(num); whole = floor(magnitude); frac = magnitude - whole; /*prints the output to the monitor*/ printf("sign: %c\nwhole number magnitude:",sign); printf("%d\nfractional part: %.2f\n", whole, frac); } By this time you shuold be comfortable with the correspondence of parameters in a function definition and arguments in a function call. In this program, list the parameters of printparts and the corresponding arguments in each function call: arguments parameters
What in main corresponds to sign in the function? Whar in main corresponds to whole in the function? Draw all the variables and their values in the memory for main and in the memory for printparts for each time it is called: main printparts (first call)
printparts (second call)
printparts (third call)
II. Modify your program so it looks like the following. You will notice that separate looks a lot like printparts, so do some cut and paste. Pay special attention to variables with asterisks in front of them in separate, like *whole, and variables with ampersands in front of them like &w in the function calls in main. Run the program. #include<stdio.h> #include<math.h> /*for fabs */ /*function prototypes*/ void separate( double num, char *sign, int *whole, double *frac); int main(void) { double a=5.3, b=-87.34, c=0; char s; /* *sign will store the sign here */ int w; /* *whole will store the whole magnitude here */ double f; /* *frac will store the fractional part here */ printf("%f\n", a); separate( &s, a, &w, &f); printf("%5c%5d%9.2f", s, w, f); printf("\n%f\n", b); separate( b, &s, &w, &f); printf("%5c%5d%9.2f", s, w, f); printf("\n%f\n",c); separate( c, &s, &w, &f); printf("%5c%5d%9.2f", s, w, f); return(0); } /*****************separate******************* /* Separates a number into three parts: a sign ( +, -, or blank) a whole number magnitude a fractional part magnitude Example: -4.25 has sign - , whole number magnitude 4, fractional part magnitude .25 This function shares the three parts with variables in main. */ void separate( double num, char *sign, int *whole, double *frac) { double magnitude; /*local variable - magnitude of num*/
/* Determine sign of num */ if (num < 0) *sign = '-'; else if (num == 0) *sign = ' '; else *sign = '+'; /* Finds magnitude of num and separates it into whole and fractional parts. */ magnitude = fabs(num); *whole = floor(magnitude); *frac = magnitude - *whole; /* nothing printed in this function */ } List the parameters of separate and the corresponding arguments in each function call. Include the * and & where they appear: arguments parameters
The variables with * in front are pointers. Technically, they hold the address of another memory location. In practice, when they have the * in front, they are referring to the value in that memory location, so they are "aliases" (extra names) for a memory location that already exists. We use them to share memory with (not just copy the values from) main. Here is a picture for the first call to separate. Fill in the values. main a b c s w f When the function is finished, the memory on the right disappears, but the new values in s, w, and f tha...