Am I properly passing parameters and passing by reference? - c

Question

I am getting no output for the grosspay and taxespaid functions for this programming assignment I am writing to keep track of employee payroll. I am just wondering if I am properly passing parameters and passing by reference, which is the method we are supposed to use. My class doesn't meet often and the book sucks so I would appreciate any advice.
#include <stdio.h>
#include <stdlib.h>
#define SIZE 5
void userinput(char name[][20], int hoursworked[], float rate[]);
void calculatepay(float rate[], int hoursworked[]);
float tax(float grosspay[]);
float totalpay(float grosspay[], float taxespaid[]);
void print(char name[][20], float rate[], int hoursworked[], float grosspay[], float sum, float taxespaid[]);
int main(){
int hoursworked[]={};
float rate[]={};
char name[][20]={};
float grosspay[]={};
float taxespaid[]={};
float sum;
userinput(name, hoursworked, rate);
calculatepay(rate, hoursworked);
sum = tax(grosspay);
totalpay(grosspay, taxespaid);
print(name, rate, hoursworked, grosspay, sum, taxespaid);
return (0);
}
void userinput(char name[][20], int hoursworked[], float rate[]){
for(int i=0; i<SIZE; i++){
printf("Enter name: ");
scanf("%s", &name[i] , 20);
if(name[i][0] == '-' && name[i][1] == '1'){
break;
}
printf("Enter hours worked: ");
scanf("%d", &hoursworked[i]);
if(hoursworked[i] == -1){
break;
}
printf("Enter hourly rate: ");
scanf("%f", &rate[i]);
if(rate[i] == -1){
break;
}
puts("\n");
}
}
void calculatepay(float rate[], int hoursworked[]){
float grosspay[]={};
for(int i=0; i<SIZE; ++i){
if(hoursworked[i]<=40){
grosspay[i] = rate[i] * hoursworked[i];
}
else{
grosspay[i] = (40*rate[i])+((hoursworked[i] - 40)*1.5*rate[i]);
}
}
}
float tax(float grosspay[]){
float taxespaid[]={};
for(int i=0; i<SIZE; ++i){
taxespaid[i] = grosspay[i]*0.2;
return taxespaid[i];
}
return 0;
}
float totalpay(float grosspay[], float taxespaid[]){
float sum = 0.0;
for (int i=0; i<SIZE; i++)
{
sum=sum+(grosspay[i] - taxespaid[i]);
}
return sum;
}
void print(char name[][20], float rate[], int hoursworked[], float grosspay[], float sum, float taxespaid[]){
for(int i=0; i<SIZE; i++){
printf("Pay to: %s\n", name[i] , 20);
if(name[i][0] == '-' && name[i][1] == '1'){
break;
}
printf("Hours worked: %d\n", hoursworked[i]);
if(hoursworked[i] == -1){
break;
}
printf("Hourly rate: %.2f\n", rate[i]);
if(rate[i] == -1){
break;
}
if(hoursworked[i]<=40){
printf("Gross Pay: %.2f\n", grosspay[i]);
}
else
{
printf("Gross Pay: %.2f\n", grosspay[i]);
printf("Base Pay: %.2f\n", rate[i]*40);
printf("Overtime Pay: %.2f\n", grosspay[i] - (rate[i]*40));
}
printf("Taxes paid: %.2f\n", taxespaid[i]);
printf("Net pay: %.2f\n\n", grosspay[i] - taxespaid[i]);
}
printf("Total paid to all employees: %.2f\n", sum);
}

Answer 1

I hate to be the bearer of bad news, but there is no pass-by-reference in C. The only method of parameter passing that C defines is pass-by-value, in 6.5.2.2p4:
In preparing for the call to a function, the arguments are evaluated, and each parameter is assigned the value of the corresponding argument.
Perhaps you intended to ask about C++, in which case... No, you're not using pass-by-reference.
Otherwise, if you intended to ask how C mimics pass-by-reference, it is by using pointers (that is, the parameters have pointer types and pointer values).
In void userinput(char name[][20], int hoursworked[], float rate[]);, for example, name, hoursworked and rate are all pointer types. The values that are passed will be pointer values. The pointer values point into the objects that are to be modified, so the same outcome is possible (that is, the changes that are made to the array are still visible once the function returns).
In case you're curious as to why this doesn't technically qualify as pass-by-reference, it's because the unary *pointer or array[subscript] (or pointer[subscript] operators are required to change the value pointed to, where-as when pass-by-reference is used you should merely be able to assign a value without those like: array = value;. It makes more sense if you look at it as a test in writing a swap function:
void swap(int x, int y) {
int temp = x;
x = y;
y = temp;
}
If you try calling this function, you will notice that it hasn't successfully swapped its arguments. If you were to use pass-by-value, those three lines would have swapped its arguments. For example, in C++:
void swap(int& x, int& y) {
int temp = x;
x = y;
y = temp;
}
This will swap the arguments. All I had to change was the function signature; I didn't have to change the way the function is used or the code in the function itself... That is pass-by-reference.

Answer 2

When I declared the variables before main() and initialised the arrays with SIZE then it worked fine :)
#define SIZE 5
void userinput(char name[][20], int hoursworked[], float rate[]);
void calculatepay(float rate[], int hoursworked[]);
float tax(float grosspay[]);
float totalpay(float grosspay[], float taxespaid[]);
void print(char name[][20], float rate[], int hoursworked[], float grosspay[], float sum, float taxespaid[]);
int hoursworked[SIZE];
float rate[SIZE];
char name[SIZE][20];
float grosspay[SIZE];
float taxespaid[SIZE];
float sum;
int main(){
userinput(name, hoursworked, rate);
calculatepay(rate, hoursworked);
sum = tax(grosspay);
totalpay(grosspay, taxespaid);
print(name, rate, hoursworked, grosspay, sum, taxespaid);
return (0);
}
void userinput(char name[][20], int hoursworked[], float rate[]){
int i;
for(i=0; i<SIZE; i++){
printf("Enter name: ");
scanf("%s", &name[i] , 20);
if(name[i][0] == '-' && name[i][1] == '1'){
break;
}
printf("Enter hours worked: ");
scanf("%d", &hoursworked[i]);
if(hoursworked[i] == -1){
break;
}
printf("Enter hourly rate: ");
scanf("%f", &rate[i]);
if(rate[i] == -1){
break;
}
puts("\n");
}
}
void calculatepay(float rate[], int hoursworked[]){
float grosspay[SIZE];
int i;
for(i=0; i<SIZE; ++i){
if(hoursworked[i]<=40){
grosspay[i] = rate[i] * hoursworked[i];
}
else{
grosspay[i] = (40*rate[i])+((hoursworked[i] - 40)*1.5*rate[i]);
}
}
}
float tax(float grosspay[]){
int i;
float taxespaid[SIZE];
for(i=0; i<SIZE; ++i){
taxespaid[i] = grosspay[i]*0.2;
return taxespaid[i];
}
return 0;
}
float totalpay(float grosspay[], float taxespaid[]){
float sum = 0.0;
int i;
for (i=0; i<SIZE; i++)
{
sum=sum+(grosspay[i] - taxespaid[i]);
}
return sum;
}
void print(char name[][20], float rate[], int hoursworked[], float grosspay[], float sum, float taxespaid[]){
int i;
for(i=0; i<SIZE; i++){
printf("Pay to: %s\n", name[i] , 20);
if(name[i][0] == '-' && name[i][1] == '1'){
break;
}
printf("Hours worked: %d\n", hoursworked[i]);
if(hoursworked[i] == -1){
break;
}
printf("Hourly rate: %.2f\n", rate[i]);
if(rate[i] == -1){
break;
}
if(hoursworked[i]<=40){
printf("Gross Pay: %.2f\n", grosspay[i]);
}
else
{
printf("Gross Pay: %.2f\n", grosspay[i]);
printf("Base Pay: %.2f\n", rate[i]*40);
printf("Overtime Pay: %.2f\n", grosspay[i] - (rate[i]*40));
}
printf("Taxes paid: %.2f\n", taxespaid[i]);
printf("Net pay: %.2f\n\n", grosspay[i] - taxespaid[i]);
}
printf("Total paid to all employees: %.2f\n", sum);
}