What is wrong with this C program using function?

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2.00/5 (1 vote)

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C++

//To find the power of a number
#include<stdio.h>
#include<conio.h>
int power(int a,int b);
int main()
{	clrscr();
	int a,b;
	printf("\nEnter the base:");
	scanf("%d",&a);
	printf("\nEnter the power:");
	scanf("%d",&b);
	printf("\nThe answer is:%d",power(a,b));
	getch();
	return 0;
}
int power(int x,int y)
{       int c;
	for(int i=1;i<=y;i++)
	c*=x;
	return c;
}

When I enter the base and exponent, I get an irrevelant answer. For example, when I type 2 for base and 3 for exponent, instead of getting 8, I get a number with many digits. Please help me. Thanks.

Posted 2-Jun-15 5:01am

Member 11735960

Updated 2-Jun-15 5:26am

Richard MacCutchan

v2

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[no name] 2-Jun-15 11:12am

Probably for the exact same reason as your other homework assignment. Learning to debug your code is also a valuable skill.

Richard MacCutchan 2-Jun-15 11:29am

What is the value of c before the for loop starts inside your power method. A quick desk check should reveal basic errors like that.

Member 11735960 2-Jun-15 11:32am

Yes. I have now initialized the value of c=1 and got the right answer. But, since I am a beginner, I don't understand how the value of variable c is something else. Can I get an explanation on that. Thanks.

CHill60 2-Jun-15 12:01pm

uninitialised variables[^]

Richard MacCutchan 2-Jun-15 12:03pm

If you don't initialise it to some value then it will just contain some random data which means your program will produce rubbish. You must initialise all your variables before you try to do anything with them.

Sascha Lefèvre 2-Jun-15 12:05pm

In C any variable that you don't explicitly initialize with a value has an undefined value. Its storage space is allocated and it has the value of what happened to be in that storage space before. It can be tricky to identify because often it happens to be zero but then sometimes it's not. So, always initialize your variables before you rely on them having a value.

CPallini 2-Jun-15 15:42pm

"But, since I am a beginner, I don't understand how the value of variable c is something else"
What makes you think a variable should be implicitely initialized with 1?
As matter of fact 0 is used more often than not for the purpose (for instance C static int are implicitely initialized with 0).

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Kornfeld Eliyahu Peter · Answer 1 · 2015-06-02T09:28:00

In C/C++ a variable that not initialized has undefined value...The reason is that the memory block used to store the variable (the variable name is actually a pointer to a memory address) may had used in the past by other variables and never cleaned...
So if the initial value of a variable is important (like in your case) you have to do that initialization...
In Microsoft compilers setting warning level to 4 will alert you about potentially uninitialized variables...
In GCC you may use -Wmaybe-uninitialized to do the same...