Shifts
Left and right shift.
Shifts is a free C Academy lesson on CoddyKit. This is lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C Academy learning path, and your progress syncs across the web and the CoddyKit app. The C Academy course includes 4 lessons in total.
Shifting Bits
The shift operators move all bits of an integer left or right by a number of positions.
Left shift is << and right shift is >>.
#include <stdio.h>
int main(void) {
unsigned x = 1;
printf("1 << 3 = %u\n", x << 3);
return 0;
}Left Shift Multiplies
Shifting left by n positions multiplies an unsigned value by 2 to the power n.
1 << 3 is 8, and 5 << 1 is 10.
#include <stdio.h>
int main(void) {
printf("5 << 1 = %u\n", 5u << 1);
printf("3 << 4 = %u\n", 3u << 4);
return 0;
}Right Shift Divides
Shifting right by n divides an unsigned value by 2 to the power n, discarding the bits that fall off the right end.
20 >> 2 is 5.
#include <stdio.h>
int main(void) {
printf("20 >> 2 = %u\n", 20u >> 2);
printf("7 >> 1 = %u\n", 7u >> 1);
return 0;
}Powers of Two
Left shifting 1 is the fastest way to generate powers of two.
1 << n is the n-th power of two.
#include <stdio.h>
int main(void) {
for (int n = 0; n < 6; n++) {
printf("2^%d = %u\n", n, 1u << n);
}
return 0;
}Visualizing a Shift
Printing the bits before and after shows how the pattern slides.
#include <stdio.h>
void print_bits(unsigned char v) {
for (int i = 7; i >= 0; i--) putchar((v >> i) & 1 ? '1' : '0');
putchar('\n');
}
int main(void) {
unsigned char v = 0b00000110;
print_bits(v);
print_bits(v << 2);
return 0;
}Extracting a Bit
To read bit number i, shift the value right by i and mask with 1.
The result is 0 or 1.
#include <stdio.h>
int main(void) {
unsigned v = 0b10110;
for (int i = 0; i < 5; i++) {
printf("bit %d = %u\n", i, (v >> i) & 1);
}
return 0;
}Building a Value Bit by Bit
You can assemble a number by shifting bits into place and combining them with OR.
#include <stdio.h>
int main(void) {
unsigned v = 0;
v |= (1u << 0);
v |= (1u << 2);
v |= (1u << 4);
printf("v = %u\n", v);
return 0;
}Signed Right Shift Caution
Right shifting a negative signed integer is implementation-defined: it may copy the sign bit.
For predictable bit operations, prefer unsigned types.
#include <stdio.h>
int main(void) {
int s = -8;
printf("-8 >> 1 = %d (implementation-defined)\n", s >> 1);
unsigned u = 8;
printf("8u >> 1 = %u\n", u >> 1);
return 0;
}Avoid Over-Shifting
Shifting by an amount greater than or equal to the type width is undefined behavior.
Shifting a 32-bit value by 32 or more is not allowed.
#include <stdio.h>
#include <limits.h>
int main(void) {
printf("unsigned has %zu bits\n", sizeof(unsigned) * CHAR_BIT);
printf("Safe shift 1u << 31 = %u\n", 1u << 31);
return 0;
}Combining Shift and Mask
Shift and mask together extract a field of several bits. Here we pull the middle 4 bits out of a byte.
#include <stdio.h>
int main(void) {
unsigned v = 0b11010110;
unsigned field = (v >> 2) & 0b1111;
printf("field = %u\n", field);
return 0;
}Fast Multiply and Add
Combining shifts lets you multiply by constants quickly. Multiplying by 10 equals shifting by 3 (times 8) plus shifting by 1 (times 2).
#include <stdio.h>
int main(void) {
unsigned x = 7;
unsigned times10 = (x << 3) + (x << 1);
printf("7 * 10 = %u\n", times10);
return 0;
}Quick Check
Test your knowledge of shifts.
Recap
You learned about shift operators:
<<shifts left and multiplies by powers of two.>>shifts right and divides by powers of two.(v >> i) & 1extracts a single bit.- Use
unsignedfor predictable shifts and never shift by the type width or more.
Learn C with an AI tutor — free
Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.
- Courses
- 39
- Lessons
- 144
Frequently Asked Questions
Is the “Shifts” lesson free?
Yes — the full text of “Shifts” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C Academy course, upgrade to CoddyKit PRO. The C Academy course includes 4 lessons in total.
What will I learn in “Shifts”?
Left and right shift. You practise C Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start C Academy?
No prior experience is required. C Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.
How long does the “Shifts” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this C Academy lesson?
Yes. Every C Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.