What is the symbol used for power?

[SiAnZ]

hi guys,
sorry... this might see a stupid question to you all as i am still a new to c++.
but i like to ask if i wanna to find the power. wat symbol do i use. as i know we use the following symbols for
addition +
substraction -
multiply *
division /
and so on. thus i like to ask wat symbol we actually use for power.
thnx and rgds,
sianz

[boxfish]

Hi,
Unfortunately, there is no symbol to raise a number to a power. You have to #include <cmath> and use its pow() function. If you're squaring a value, it's probably best to just use the * operator and multiply the value by itself.
Hope this helps.

[SiAnZ]

ok
thanx alot.
now actully i done the program
but the program seems like got some bugs. like for example 17^23 mod 23 = 17 but i got -6. den 21^17 mod 61 = 29 but i got -59. den if i do 2^3 mod 5 =3 which i get the rite answer. the problem is like if i use big number to do, the output i got is wrong but if i use small number, i can get the correct input. can anyone help?

#include <stdio.h> 
#include <math.h>  
using namespace std; 
int main(void) 
{     
int integer1; //first number to be input     
int integer2; //2nd number to be input     
int integer3; //modular to be input     
int integer4; //do the power function     
int sum; //varible of thing to be stalled in          
 
printf( "pls enter number: \n" ); //promt for number     
scanf("%d", &integer1);         
 
printf( "pls enter power: \n" ); //promt for power     
scanf("%d", &integer2);          
 
printf( "pls enter modular: \n" ); //promt for modular     
scanf("%d", &integer3);          
 
integer4 = pow(integer1,integer2);     
//scanf("%d", &integer4);          
 
sum = integer4 % integer3;     
printf("ans is %d\n", sum); //print sum          
return 0;  } 
 

[Ganon11]

How large is 17^23, or 23^17?

Hint: The largest number an int can carry is 2,147,483,647.

[SiAnZ]

actually i wan to calculate 17^ 23 mod 23 and 21^17 mod 61 etc... so if the largest int can carry, does it mean i have to use others insted of int?

[Banfa]

No if you are using modulus division you can use the identity

(a * b) mod c = ((a mod c) * (b mod c)) mod c

If it is a power calculation

(a ^ b) mod c = ((a mod c) ^ b) mod c

At first this doesn't seem useful because in your examples c > a so a mod c == a but if instead of doing the ^ as a single function call you treat it as multiple multiplication (which you can since you are using integers so b is always an integer but we are constraining it to be always positive too) then you can do something like this.

(a ^ b) mod c = ((a mod c) ^ b) mod c

if b == 3

(a ^ b) mod c = (a * a * a) mod c

but

(a * b) mod c = ((a mod c) * (b mod c)) mod c

and

a * b * c = (a * b) * c

so

(a ^ b) mod c = ((((a mod c) * (a mod c)) mod c) * (a mod c)) mod c

Basically you will have to do the power calculation yourself using a loop and at every interim result (iteration) you apply the modulus to keep the values in range of your integers.

This should work as long as c-1 < sqrt(MAX_INT)



Of course another option is to use 64 bit integers that mamny platforms support today.

[Laharl]

Also, use <cstdio> and <cmath> rather than <stdio.h> and <math.h>, respectively. The .h style for C standard libraries is deprecated as of 1998 or so. Not a huge deal, just a nit to pick.