Beginner in C++ need help

[jasson118]

calculate the power of 2 integers. For example, power(2,3)=8,
power(3,2)=9,po wer(4,0)=1. Not allow use power math function.Two
integers are read from input by scanf. The program must produce an
error message when the user enter a negative number, able to calculate
the powers until terminate by user "by entering ctl-Z". output show
both input integer and the result. program 1 use "while" statement to
do the calculation.pro gram 2 use "do-while"statement to do the
calculation. program 3 use "for"statem ent to do the calculation.

The following is what I did for the "for" statement. It's not working.
I also missed the part of showing an error message when the user enter
a negative number

#include "stdio.h"
int main()
{
int a,b,loop,result ;
if ((scanf("%d%d", &a,&b)==EOF) )
{
printf("\n Terminate by user\n");
break;
}
else
printf("Enter the base and power:\n");
scanf("%d%d",&a ,&b);
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf(" Base:",a);
printf(" power:",b);
printf(" result:",result );
return 0;
}

[John Harrison]

ja*******@hotma il.com wrote:

calculate the power of 2 integers. For example, power(2,3)=8,
power(3,2)=9,po wer(4,0)=1. Not allow use power math function.Two
integers are read from input by scanf. The program must produce an
error message when the user enter a negative number, able to calculate
the powers until terminate by user "by entering ctl-Z". output show
both input integer and the result. program 1 use "while" statement to
do the calculation.pro gram 2 use "do-while"statement to do the
calculation. program 3 use "for"statem ent to do the calculation.

The following is what I did for the "for" statement. It's not working.
I also missed the part of showing an error message when the user enter
a negative number

#include "stdio.h"
int main()
{
int a,b,loop,result ;
if ((scanf("%d%d", &a,&b)==EOF) )
{
printf("\n Terminate by user\n");
break;
}
else
printf("Enter the base and power:\n");
scanf("%d%d",&a ,&b);
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf(" Base:",a);
printf(" power:",b);
printf(" result:",result );
return 0;
}

It's not working for several reasons.

1)

scanf("%d %d",&a,&b);

Note the space between the two %d

2)

for (loop=1; loop<=b; loop++)
{
result=result*a ;
}

This loop is fine, it's says multiply result by a and do it b times,
which is exactly what you want. But ask yourself these questions. What
is the value of result before you start this loop? What should it be
before you start this loop?

3)

The main mistake though is something that isn't very clear from the
program description. This program needs two loops, one inside the other.

The outer loop is, loop until the user hits Ctrl+Z or enters a negative
number. The inner loop is the one you've already written to calculate
result.

It's not clear from the instructions about use a for loop, use a while
loop which loop is being talked about. I would guess the inner loop.

So I would write something like this

for (;;) // loop forever
{
get input
if (Ctrl+Z or negative number)
break; // stop looping forever
do calculation
print results
}

john

[osmium]

<ja*******@hotm ail.comwrote:

calculate the power of 2 integers. For example, power(2,3)=8,
power(3,2)=9,po wer(4,0)=1. Not allow use power math function.Two
integers are read from input by scanf. The program must produce an
error message when the user enter a negative number, able to calculate
the powers until terminate by user "by entering ctl-Z". output show
both input integer and the result. program 1 use "while" statement to
do the calculation.pro gram 2 use "do-while"statement to do the
calculation. program 3 use "for"statem ent to do the calculation.

The following is what I did for the "for" statement. It's not working.
I also missed the part of showing an error message when the user enter
a negative number

#include "stdio.h"
int main()
{
int a,b,loop,result ;
if ((scanf("%d%d", &a,&b)==EOF) )
{
printf("\n Terminate by user\n");
break;
}
else
printf("Enter the base and power:\n");
scanf("%d%d",&a ,&b);
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf(" Base:",a);

You misunderstand the requirements for the parameters given to printf.

Try something like this:
printf("Base %d \n", a);

printf(" power:",b);
printf(" result:",result );
return 0;
}

I would isolate the computation in a function, then you can use the same
"shell" for the three programs you have to write. The outer shell is an
"infinite" loop looking for EOF or certain cases of bad input. If you
isolate the computation it is simply cut and paste to come up with the
repetitive part of the three programs.

Your instructor allows you to ignore other forms of bad input: non-digit
input for example, and numbers too large. In general n^m will not fit in an
integer.

[jasson118]

#include "stdio.h"
#include "assert.h"
int main()
{
int a,b,loop,result ,ret;
printf("Base:") ;
ret=scanf("%d", &a);
printf("power:" );
scanf("%d",&b);
if(ret==0)
{ //could not read from std input
fprintf(stderr, "Invalid input\n");
}
else if(ret==EOF)
{ //read from file and EOF reached
fprintf(stderr, "EOF reached\n");//or silentlty return
return -1;
}
else
{ //read is success
assert(ret==1);
if(a<0)
{ // user entered negative value
fprintf(stderr, "No negative value please\n");
return -1;
}
}

result=1;
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf("Base: %d \n", a);
printf("power:% d \n", b);
printf("result: %d \n",result);
return 0;
}

I made some changes to my code.
The program works fine, but just unable to continue testing after I
press any key, the window closes.

[jasson118]

can anyone help?

[Alf P. Steinbach]

* ja*******@hotma il.com:

#include "stdio.h"
#include "assert.h"
int main()
{
int a,b,loop,result ,ret;
printf("Base:") ;
ret=scanf("%d", &a);
printf("power:" );
scanf("%d",&b);
if(ret==0)
{ //could not read from std input
fprintf(stderr, "Invalid input\n");
}
else if(ret==EOF)
{ //read from file and EOF reached
fprintf(stderr, "EOF reached\n");//or silentlty return
return -1;
}
else
{ //read is success
assert(ret==1);
if(a<0)
{ // user entered negative value
fprintf(stderr, "No negative value please\n");
return -1;
}
}

result=1;
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf("Base: %d \n", a);
printf("power:% d \n", b);
printf("result: %d \n",result);
return 0;
}

I made some changes to my code.
The program works fine, but just unable to continue testing after I
press any key, the window closes.

Run the program from the command line (Google "command line").

By the way, why don't you use the C++ i/o facilities?

The program above is C, with nothing C++-specific.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[John Harrison]

>

I made some changes to my code.
The program works fine, but just unable to continue testing after I
press any key, the window closes.

Well either you need to run the program again. Or if you don't want to
do that it's like my earlier post said, you need a second outer loop in
your program.

john

[dervaish]

You are asking it in wrong forum, just ask it in comp.lang.c forum

[Alan Johnson]

ja*******@hotma il.com wrote:

#include "stdio.h"
#include "assert.h"
int main()
{
int a,b,loop,result ,ret;

Everything from here ....

printf("Base:") ;
ret=scanf("%d", &a);
printf("power:" );
scanf("%d",&b);
if(ret==0)
{ //could not read from std input
fprintf(stderr, "Invalid input\n");
}
else if(ret==EOF)
{ //read from file and EOF reached
fprintf(stderr, "EOF reached\n");//or silentlty return
return -1;
}
else
{ //read is success
assert(ret==1);
if(a<0)
{ // user entered negative value
fprintf(stderr, "No negative value please\n");
return -1;
}
}

result=1;
for (loop=1; loop<=b; loop++)
{
result=result*a ;
}
printf("Base: %d \n", a);
printf("power:% d \n", b);
printf("result: %d \n",result);

down to here needs to be inside an "infinite" loop. You typically see
this done as John Harrison mentioned earlier in the thread:

for (;;)
{
// Body of the loop
}

The reason a for loop is used for that is because some compilers issue a
warning when the condition of a while loop is always true.

return 0;
}

I made some changes to my code.
The program works fine, but just unable to continue testing after I
press any key, the window closes.

On an unrelated note, this thread is a perfect example of the correct
way to ask for homework help. Usenet needs "sticky" posts. :-)

--
Alan Johnson