Question..

scjeff05 · 02-06-2006, 09:38 AM

Hey, im new to the forums and new to programming in linux. I hope to learn a lot from this forum. Im not sure if im posting this is the correct place, but just let me know if im not.
Ok, im writing a simple program in C and i keep getting this error message
new1.c: In function `void enterdata(float&, float&, float&)':
new1.c:21: error: cannot convert `float' to `const char*' for argument `1' to `int scanf(const char*, ...)'
new1.c:23: error: cannot convert `float' to `const char*' for argument `1' to `int scanf(const char*, ...)'
new1.c:25: error: cannot convert `float' to `const char*' for argument `1' to `int scanf(const char*, ...)'
new1.c: In function `void printresults(float&)':
new1.c:38: error: cannot convert `float' to `const char*' for argument `1' to `int printf(const char*, ...)'

here is the code

Code:

int main()
{
float gascost, milesoftrip, milespergallon, totalcosta;
float calculatecost(float gascost,float milesoftrip,float milespergallon);
void enterdata(float &gascost, float &milesoftrip, float &milespergallon);
void printresults(float &totalcosta);

enterdata(gascost, milesoftrip, milespergallon);
totalcosta=calculatecost(gascost,milesoftrip,milespergallon);

printresults(totalcosta);
return 0;
}
void enterdata(float &gascost, float &milesoftrip, float &milespergallon)
{
printf("Enter GAS Cost ");
scanf(gascost);
printf("Enter MILES ");
scanf(milesoftrip);
printf("Enter MPG ");
scanf(milespergallon);

}
float calculatecost(float gascost,float milesoftrip,float milespergallon)
{
float totalcost;
totalcost = (milesoftrip/milespergallon) * gascost;
return totalcost;

}
 
void printresults(float &totalcosta)
{
printf(totalcosta);
}

its probably a mess because all i have been taught it c++, but if anyone could help that would be great. thanks in advance

graemef · 02-06-2006, 10:10 AM

scanf expects at least two argumants. The first is a format string that describes the variables that are to be read in and the remaining arguments are pointers to the the variables that you wich to set up so:

Code:

scanf(gascost);

should be

Code:

scanf("%f",&gascost);

scjeff05 · 02-06-2006, 10:25 AM

Thanks!!!!

scjeff05 · 02-06-2006, 10:29 AM

One more quick question, i need to create a makefile, i know what goes in it, i just dont know how to create it.

dmail · 02-06-2006, 10:34 AM

I didn't think function prototypes inside main would be allowed or work, but it compiles and works fine. Maybe it just me? but I think it's bad practice, unless someone can tell me a viable reason for doing it?

Code:

int main()
{
float gascost, milesoftrip, milespergallon, totalcosta;
float calculatecost(float gascost,float milesoftrip,float milespergallon);
void enterdata(float &gascost, float &milesoftrip, float &milespergallon);
void printresults(float &totalcosta);
....

I would normally write it like:

Code:

float calculatecost(float,float,float);
void enterdata(float&, float&, float&);
int main()....

plus this is "C" correct?
the enterdata func accepts float refs? are these meant to be pointers?

scjeff05 · 02-06-2006, 11:15 AM

ugh, now its saying this
new3.c: In function `main':
new3.c:7: error: syntax error before '&' token
new3.c:8: error: syntax error before '&' token
new3.c: At top level:
new3.c:17: error: syntax error before '&' token
new3.c: In function `enterdata':
new3.c:20: error: `gascost' undeclared (first use in this function)
new3.c:20: error: (Each undeclared identifier is reported only once
new3.c:20: error: for each function it appears in.)
new3.c:22: error: `milesoftrip' undeclared (first use in this function)
new3.c:24: error: `milespergallon' undeclared (first use in this function)
new3.c: At top level:
new3.c:34: error: syntax error before '&' token
new3.c: In function `printresults':
new3.c:36: error: `totalcosta' undeclared (first use in this function)

im really new to linux and no one has taught me how to do this

but here is the code

Code:

#include <stdio.h>

int main()
{
float gascost, milesoftrip, milespergallon, totalcosta;
float calculatecost(float gascost,float milesoftrip,float milespergallon);
void enterdata(float &gascost, float &milesoftrip, float &milespergallon);
void printresults(float &totalcosta);

enterdata(gascost, milesoftrip, milespergallon);
totalcosta=calculatecost(gascost,milesoftrip,milespergallon);

printresults(totalcosta);
return 0;
}

void enterdata(float &gascost, float &milesoftrip, float &milespergallon)
{
printf("Enter GAS Cost ");
scanf("%f",&gascost);  
printf("Enter MILES ");  
scanf("%f",&milesoftrip);
printf("Enter MPG ");
scanf("%f",&milespergallon);
}

float calculatecost(float gascost,float milesoftrip,float milespergallon)
{
float totalcost;
totalcost = (milesoftrip/milespergallon) * gascost;
return totalcost;
}

void printresults(float &totalcosta)
{
scanf("%f",&totalcosta);
}

scjeff05 · 02-06-2006, 11:17 AM

yeah, see thats the problem, i have learned the basics of c++, then i get this project in C and now i have no clue what to do...so lost..., well if anyone can help me some more that would be great

dmail · 02-06-2006, 11:26 AM

lol them errors sort of answer my questions. C doesn't have refs but uses pointers, so I you change it to this it should work, havn't tested it but it should be ok. If you dont understand what ive done just ask and ill go through it.

<edited see next post>

to pass by reference(different than a reference) you need to pass the address of the variable(if it's not already a pointer) and accept a pointer in the func:
example
int a;the variable
foo(int*);func prototype

foo(&a);this passes the address of a to foo.

dmail · 02-06-2006, 11:35 AM

Hmmm just noticed you said

Quote:

...then i get this project in C...

Please advise if its a school coursework etc. in future ;(

scjeff05 · 02-06-2006, 12:42 PM

No, im taking these projects off some cd that i got a wile back, it goes along with a book but i dont know where i placed it, the only class i took on the subject was C++ in high school, but that was some time ago and i cant remeber half that stuff.

dmail · 02-06-2006, 01:01 PM

Quote:

Originally Posted by scjeff05

No, im taking these projects off some cd that i got a wile back, it goes along with a book but i dont know where i placed it, the only class i took on the subject was C++ in high school, but that was some time ago and i cant remeber half that stuff.

Ok Im sorry.
Did you see the post i made earlier or would you like me to post it again?

scjeff05 · 02-06-2006, 01:08 PM

Im not sure, i understand how it works, i just dont understand how to apply it to the code.

graemef · 02-06-2006, 01:16 PM

Okay,

you are confusing & with *

The * says this will be a pointer to a memory location
Whereas & says take this variable and return the address.

So when you define a function you will tell it to expect a pointer as follows:

Code:

void enterdata(float *gascost
              ,float *milesoftrip
              ,float *milespergallon);

When you call the function you want to pass the address of the variables as follows:

Code:

enterdata(&gascost, &milesoftrip, &milespergallon);

Don't worry it takes a while to really understand what they do and mean but because they are so important in C / C++ it is worth spending the time to understand them.

dmail · 02-06-2006, 01:21 PM

this is how i would write it plus added a deference to show how its done

Code:

#include <stdio.h>
//function prototypes
float calculatecost(float ,float ,float* );
void enterdata(float*, float* , float* );
void printresults(float);

int main()
{
	float gas, miles, mpg;
	//pass by reference instead of value using the "&" which
	//gives the address
	enterdata(&gas, &miles, &mpg);
	printresults( calculatecost(gas,miles,&mpg) );
return 0;
}

void enterdata(float* gas, float* miles, float* mpg)
{
	printf("Enter GAS Cost ");
	//these are already pointers so no need to pass the address
	scanf("%f",gas);  
	printf("Enter MILES ");  
	scanf("%f",miles);
	printf("Enter MPG ");
	scanf("%f",mpg);
}

	//lets just pass by reference mpg to show how to get the 
	//value from a pointer
float calculatecost(float gas,float milesp,float* mpg)
{
	//"*" deferences a pointer and gets the value of the variable 
	//it points to
	//remove the temp as there was no need for it
	return ((miles / *mpg) * gas);
}

void printresults(float cost)
{
	printf("cost was %f\n",cost);
}

dmail · 02-06-2006, 01:32 PM

heres a post i made a while ago about pointers it may help
http://www.linuxquestions.org/questi...d.php?t=383082