1. <iostream> – Input/Output Operations
| Keyword / Function | Function / Purpose |
|---|---|
cout |
Prints output to the console. |
cin |
Takes input from the user. |
endl |
Moves cursor to the next line (like \n). |
cerr |
Prints error messages to standard error. |
clog |
Prints log messages to standard error. |
2. <cmath> – Math Functions
| Function / Keyword | Function / Purpose |
|---|---|
abs(x) |
Absolute value of x. |
pow(x, y) |
x raised to the power y. |
sqrt(x) |
Square root of x. |
ceil(x) |
Smallest integer ≥ x. |
floor(x) |
Largest integer ≤ x. |
round(x) |
Rounds x to nearest integer. |
sin(x), cos(x), tan(x) |
Trigonometric functions (angle in radians). |
log(x) |
Natural logarithm (base e) of x. |
exp(x) |
e raised to the power x. |
3. <string> – String Operations
| Function / Keyword | Function / Purpose |
|---|---|
std::string |
Declares a string variable. |
.length() / .size() |
Returns length of string. |
.append() |
Adds text to end of string. |
.insert(pos, str) |
Inserts string at position. |
.erase(pos, len) |
Deletes part of string. |
.find(str) |
Finds first occurrence of substring. |
.substr(pos, len) |
Returns substring starting at position. |
.c_str() |
Converts string to C-style char array. |
.compare(str) |
Compares two strings. |
4. <vector> – Dynamic Arrays
| Function / Keyword | Function / Purpose |
|---|---|
std::vector<Type> |
Declares a dynamic array (vector). |
.push_back(value) |
Adds element at the end. |
.pop_back() |
Removes last element. |
.size() |
Returns number of elements. |
.empty() |
Checks if vector is empty. |
[index] |
Access element at given index. |
.at(index) |
Access element with bounds checking. |
.clear() |
Removes all elements. |
5. <algorithm> – Algorithms for Containers
| Function / Keyword | Function / Purpose |
|---|---|
sort(start, end) |
Sorts elements in ascending order. |
reverse(start, end) |
Reverses elements. |
max(a, b) |
Returns maximum of two values. |
min(a, b) |
Returns minimum of two values. |
swap(a, b) |
Swaps two values. |
count(start, end, value) |
Counts occurrences of value. |
find(start, end, value) |
Finds first occurrence of value. |
6. <fstream> – File Handling
| Function / Keyword | Function / Purpose |
|---|---|
std::ifstream |
Opens a file for reading. |
std::ofstream |
Opens a file for writing. |
std::fstream |
Opens a file for reading & writing. |
.open(filename) |
Opens a file with given name. |
.close() |
Closes the file. |
.is_open() |
Checks if file is open. |
.getline() |
Reads a line from a file. |
<< / >> |
Writes to / reads from file (like cin / cout). |
7. <cstdlib> – Standard Library Utilities
| Function / Keyword | Function / Purpose |
|---|---|
rand() |
Generates a random integer. |
srand(seed) |
Sets seed for random number generator. |
exit(status) |
Terminates the program with a status code. |
abs(x) |
Absolute value of integer (similar to <cmath>). |
atoi(str) |
Converts string to integer. |
atof(str) |
Converts string to float. |
8. <ctime> – Date and Time
| Function / Keyword | Function / Purpose |
|---|---|
time(NULL) |
Returns current time in seconds since epoch. |
clock() |
Returns processor time used by program. |
difftime(t1, t2) |
Returns difference in seconds between two times. |
localtime() |
Converts time to local time structure. |
strftime() |
Formats time as a string. |
9. <iomanip> – Input/Output Manipulators
| Function / Keyword | Function / Purpose |
|---|---|
std::setw(n) |
Sets width of output field. |
std::setprecision(n) |
Sets decimal precision for floating-point numbers. |
std::fixed |
Displays floating-point numbers in fixed format. |
std::scientific |
Displays floating-point numbers in scientific notation. |
std::setfill(c) |
Fills empty space with character c. |
