operator << used in for loop and if statement

[anurag117]

hello, i came across some c++ codes using following statements :

for(int i=0;i<(1<<n);i++){
some statements
..............}

and

if(n&(1<<i)){
statement }

and

int dp[1<<21];

now i dont understand what 1<<n means...i have never used << operator like this before and was not able to find anything about it on the net

[vlad from moscow]

It is bitwise shift operator. It shifs the value of the left operand the number of times specified by the right operand.

[tcs]

1 << n <=> 2^n, where ^ means power of.
Since at least 20 years modern compilers will internally translate 2^n to this bitshift if supported by the CPU (nearly every CPU does support it).

int dp[1<<21]; is interesting because it addresses a really big array with at least sizeof(int) * (1 + 2^21) bytes.

[cire]

1 << n <=> 2^n, where ^ means power of.

It should be noted, however that the caret does not mean power of in C++, so

Since at least 20 years modern compilers will internally translate 2^n to this bitshift

would be wrong. As 2^n has a decidedly different meaning than 2 to the power of n in C++.

int dp[1<<21]; is interesting because it addresses a really big array with at least sizeof(int) * (1 + 2^21) bytes.

Well, it defines one with exactly sizeof(int*)*(1<<21) bytes, anyway.

[anurag117]

thankyou all...it helped a lot

[tcs]

@cire: Ok, you're right with the meaning of ^ in C++. But I've defined it to the power of. So in this context its quite right the power of. Your other statements I agree with you.