should this work

A

amanayin

The program is simple and i know i should use switch instead of if
but i done it this way for a reason. But i am not sure if it should work
when i was compiling it i was getting warning messages but then suddenly
it started working. The reason i wrote the program was to get used to using
functions, if statement and logical operators.

/* ARITH1.C SIMPLE CALCULATOR PROGRAM */

#include<stdio.h>

float add(float a, float b);
float sub(float a, float b);
float multi(float a, float b);
float div(float a, float b);
float per(float a, float b);
char call(float math);
float a,b,c,math;
char d;

int main(void)
{
printf("Enter 1st value: ");
scanf("%f",&a);
printf("Enter 2nd value: ");
scanf("%f",&b);

call(d);
return 0;
}


char call(float math)
{

while(d != 'q'){
printf("Enter operand or q to exit: ");
scanf("%s",&d);

if(d == '+')
{ math = add(a,b); }
if(d == '-')
{ math = sub(a,b); }
if(d == '*')
{ math = multi(a,b); }
if(d == '/')
{ math = div(a,b); }
if(d == '%')
{ math = per(a,b); }
if(d != '+' && d != '-' && d != '*' && d != '/' && d != '%' && d != 'q')
{ printf("Operand not accepted try again\n"); continue; }
if(d == 'q')
{ puts("Exiting"); break; }
printf("Total is %.3f\n",math);
}
return math;
}

float add(float a, float b)
{
c = a + b;
return c;
}

float sub(float a,float b)
{
c = a - b;
return c;
}

float multi(float a, float b)
{
c = a * b;
return c;
}

float div(float a, float b)
{
c = a / b;
return c;
}

float per(float a, float b)
{
c = a * b / 100;
return c;
}
 
M

Mark Gordon

The program is simple and i know i should use switch instead of if
but i done it this way for a reason. But i am not sure if it should
work when i was compiling it i was getting warning messages but then
suddenly it started working. The reason i wrote the program was to get
used to using functions, if statement and logical operators.

/* ARITH1.C SIMPLE CALCULATOR PROGRAM */

#include<stdio.h>

float add(float a, float b);
float sub(float a, float b);
float multi(float a, float b);
float div(float a, float b);
float per(float a, float b);
char call(float math);
float a,b,c,math;
char d;
Click to expand...

Why declare these as globals? It is far easier to get things right if
you minimise the scope of variables.
int main(void)
{
printf("Enter 1st value: ");
scanf("%f",&a);
printf("Enter 2nd value: ");
scanf("%f",&b);

call(d);
Click to expand...

call is declared as taking a float but you are passing a character. You
compiler should have warned you about this. Also d has not been
initialised and by passing it as a parameter you are evaluating it.
return 0;
}


char call(float math)
Click to expand...

You never use the value passed in so why have it as a parameter?
{

while(d != 'q'){
Click to expand...

d still has not been initialised so absolutely ANYTHING could happen
here.
printf("Enter operand or q to exit: ");
Click to expand...

This may not actually be printed before the scanf. Read the FAQ for
further information.
scanf("%s",&d);
Click to expand...

%s fetches a null terminated string, not a single character but you are
only passing the address of a single character, so this is guaranteed to
overflow on any input.
if(d == '+')
{ math = add(a,b); }
if(d == '-')
{ math = sub(a,b); }
if(d == '*')
{ math = multi(a,b); }
if(d == '/')
{ math = div(a,b); }
if(d == '%')
{ math = per(a,b); }
if(d != '+' && d != '-' && d != '*' && d != '/' && d != '%' && d
!= 'q')
{ printf("Operand not accepted try again\n"); continue; }
if(d == 'q')
{ puts("Exiting"); break; }
Click to expand...

The break will exit the while loop making the condition completely
pointless once all the other bugs are fixed.
printf("Total is %.3f\n",math);
}
return math;
}

float add(float a, float b)
{
c = a + b;
return c;
Click to expand...

Why are you using a global variable here? Why not just use
return a + b;
}
Click to expand...

<snip>

I seriously think you need to do work through a decent text book. You
will find recommendations in the FAQ for comp.lang.c (Q 18.10)
 
I

Irrwahn Grausewitz

amanayin said:
The program is simple and i know i should use switch instead of if
but i done it this way for a reason. But i am not sure if it should work
when i was compiling it i was getting warning messages but then suddenly
it started working. The reason i wrote the program was to get used to using
functions, if statement and logical operators.

/* ARITH1.C SIMPLE CALCULATOR PROGRAM */

#include<stdio.h>

float add(float a, float b);
float sub(float a, float b);
float multi(float a, float b);
float div(float a, float b);
Click to expand...

'div' is a bad name for a function, because there's a function with the
same name declared in stdlib.h. Not a problem yet, but if you have to
include stdlib.h later the two definitions will clash. Call it 'divide'
or the like.
float per(float a, float b);
char call(float math);
float a,b,c,math;
char d;

int main(void)
{
printf("Enter 1st value: ");
scanf("%f",&a);
printf("Enter 2nd value: ");
scanf("%f",&b);

call(d);
Click to expand...

You pass a character to a funtion that expects a double.
return 0;
}


char call(float math)
Click to expand...

1. Why do you pass an argument at all?
2. Your function is declared to return a character.
Later on you return a double.
{

while(d != 'q'){
printf("Enter operand or q to exit: ");
scanf("%s",&d);
Click to expand...

The "%s" conversion specifier is for reading strings. It will store any
user input plus a null character at &d, but there's only space for one
character. Use "%c" (overkill) or just d = getchar(); (recommended).
if(d == '+')
{ math = add(a,b); }
if(d == '-')
{ math = sub(a,b); }
if(d == '*')
{ math = multi(a,b); }
if(d == '/')
{ math = div(a,b); }
if(d == '%')
{ math = per(a,b); }
if(d != '+' && d != '-' && d != '*' && d != '/' && d != '%' && d != 'q')
{ printf("Operand not accepted try again\n"); continue; }
if(d == 'q')
{ puts("Exiting"); break; }
printf("Total is %.3f\n",math);
}
return math;
Click to expand...

See above.
}

float add(float a, float b)
{
c = a + b;
return c;
}

float sub(float a,float b)
{
c = a - b;
return c;
}

float multi(float a, float b)
{
c = a * b;
return c;
}

float div(float a, float b)
Click to expand...

See above.
{
c = a / b;
return c;
}

float per(float a, float b)
{
c = a * b / 100;
return c;
}
Click to expand...

Besides of the mentioned problems your code looks fine AFAICT.

HTH

Regards
 
O

osmium

amanayin said:
The program is simple and i know i should use switch instead of if
but i done it this way for a reason. But i am not sure if it should work
when i was compiling it i was getting warning messages but then suddenly
it started working. The reason i wrote the program was to get used to using
functions, if statement and logical operators.

/* ARITH1.C SIMPLE CALCULATOR PROGRAM */

#include<stdio.h>

float add(float a, float b);
float sub(float a, float b);
float multi(float a, float b);
float div(float a, float b);
float per(float a, float b);
char call(float math);
float a,b,c,math;
char d;

int main(void)
{
printf("Enter 1st value: ");
scanf("%f",&a);
printf("Enter 2nd value: ");
scanf("%f",&b);

call(d);
Click to expand...

I wouldn't do that. You are passing call() a char when it wants a float.
There is not reson to do that in code such as this. It may have no bearing
on the problem you say you *used to have*.
 
M

Mark Gordon

d has been initialized to 0 automatically on declaration.
Click to expand...

You're right. I saw so many problems in how the code was written I saw
more problems than were there.
 
P

pete

Irrwahn said:
'div' is a bad name for a function,
because there's a function with the same name declared in stdlib.h.
Not a problem yet,
Click to expand...

I think it is a problem.

My copy of the C89 last draft, has this:
4.1.2 Standard headers
All external identifiers declared in any of the headers are
reserved, whether or not the associated header is included.
 
B

Barry Schwarz

Why declare these as globals? It is far easier to get things right if
you minimise the scope of variables.


call is declared as taking a float but you are passing a character. You
compiler should have warned you about this. Also d has not been
Click to expand...

Why would you expect a warning when the conversion from char to float
is automatic and well defined?



<<Remove the del for email>>
 
I

Irrwahn Grausewitz

pete said:
I think it is a problem.
Click to expand...

You're right. I should have said: "Possibly not causing real trouble
yet, but definitely a problem ..."

Regards
 
A

amanayin

Irrwahn Grausewitz wrote:

snip
The "%s" conversion specifier is for reading strings. It will store any
user input plus a null character at &d, but there's only space for one
character. Use "%c" (overkill) or just d = getchar(); (recommended).
Click to expand...

If i use d = getchar(); or %c instead of %s i get the
following out put
Enter operand or q to quit: operand not accepted try again:
change it back to %s it works fine
 
M

Mark Gordon

so what should i change it to?
Click to expand...

When you want a variable within a function you should declare it within
that function.

From memory something like

void call(void)
{
float math;
/* do stuff */
}

would have been better.
 
I

Irrwahn Grausewitz

amanayin said:
Irrwahn Grausewitz wrote:

snip

If i use d = getchar(); or %c instead of %s i get the
following out put
Enter operand or q to quit: operand not accepted try again:
Click to expand...
Er, yes, that's because scanf left some unread input (the newline, at
least) after the second value was read. In the code below this is
fixed (see function drain_stdin()).
change it back to %s it works fine
Click to expand...
And this still invokes undefined behaviour. d can only hold one
character, thus you produce a buffer overrun.

In the code below the global variables are eliminated and the definition
of call is fixed. I left the if-chain unchanged, as you said it was an
exercise. Note also the use of fflush(), lookup the c.l.c-FAQ Q12.4 for
an explanation. You should also consider to use double instead of
float; usually there's no reason to use float at all.

Here's the improved code:

/* ARITH2.C SIMPLE CALCULATOR PROGRAM */

#include<stdio.h>

float add(float a, float b);
float sub(float a, float b);
float multi(float a, float b);
float div(float a, float b);
float per(float a, float b);
void call( float a, float b );
void drain_stdin( void );

int main(void)
{
float a, b;

printf("Enter 1st value: ");
fflush( stdout );
scanf("%f",&a);
printf("Enter 2nd value: ");
fflush( stdout );
scanf("%f",&b);

call( a, b );
return 0;
}


void call( float a, float b )
{
char d = 0;
float math = 0.0;

while( d != 'q' )
{
printf("Enter operand or q to exit: ");
fflush( stdout );
drain_stdin();
scanf( "%c", &d );

if(d == '+')
{ math = add(a,b); }
if(d == '-')
{ math = sub(a,b); }
if(d == '*')
{ math = multi(a,b); }
if(d == '/')
{ math = div(a,b); }
if(d == '%')
{ math = per(a,b); }
if(d != '+' && d != '-' && d != '*' && d != '/' &&
d != '%' && d != 'q')
{ printf("Operand not accepted try again\n"); continue; }
if(d == 'q')
{ puts("Exiting"); break; }
printf("Total is %.3f\n", math);
}
return;
}

void drain_stdin( void )
{
while ( getchar() != '\n' )
/*do nothing*/;
return;
}

float add(float a, float b)
{
return a + b;
}

float sub(float a,float b)
{
return a - b;
}

float multi(float a, float b)
{
return a * b;
}

float div(float a, float b)
{
return a / b;
}

float per(float a, float b)
{
return a * b / 100;
}


HTH
Regards
 

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