# C Program to Find Power of a Number Using Function

We will write a C program to find the power of a number using a function. First, we will use the pre-defined function pow(), and later we will develop a user-defined function.

## C program to find the power of a number using pow() function

In C language, the pow() is a pre-defined function that is used to calculate the power of the number. It takes two arguments. It is defined in the header file “`math.h`”. SO, to use the pow() function, we must include this header file in our program.

Function prototype:- `pow(x,y);`

The function pow() calculates the power of y. If the x is negative, y must be an integer. If the x is zero, y must be a positive number.

``````#include<stdio.h>
#include<math.h>
int main()
{
int num1, num2;

printf("Enter base and power: ");
scanf("%d %d",&num1, &num2);

printf("Result = %.2f",pow(num1, num2));

return 0;
}``````

Output for the different test-cases:-

Enter base and power: 2 5
Result = 32.00

Enter base and power: 5 4
Result = 625.00

## Using a user-defined function

We can also write a C program to find the power of a number without using pow(). In the below program power() is a user-defined function that calculates the power of a number. Previously we have already written a program to find the power of a number using loops. Based on that program we can write the same using function.

Prerequisites for this program:- Introduction to Function in C, User-defined Functions in C, C Program Using Functions Example

``````#include<stdio.h>
long power(int a, int b);

int main()
{
int num1, num2;

printf("Enter base and power: ");
scanf("%d %d",&num1, &num2);

long result = power(num1, num2);
printf("The result = %ld", result);

return 0;
}

// User-defined function to calculate power
long power(int a, int b)
{
long result = 1;
for(int i=1; i<=b; i++)
{
result *= a;
}
return result;
}``````

Output for the different test-cases:-

Enter base and power:` 3 3`
The result = 27

Enter base and power:` 7 2`
The result = 49

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