**Backtracking** is a general *algorithmic technique for solving problems that involve searching for a solution among a large set of possibilities. It works by incrementally building a solution and undoing previous choices when they lead to a dead-end* until a valid solution is found. In C language, **backtracking** can be implemented using recursion.

Here’s an example of a **backtracking algorithm** in C language:

```
#include <stdio.h>
#define N 4
int board[N][N]; // N x N chess board
// Function to print the solution
void printSolution() {
int i, j;
for (i = 0; i < N; i++) {
for (j = 0; j < N; j++)
printf(" %d ", board[i][j]);
printf("\n");
}
}
// Function to check if it is safe to place the queen at board[row][col]
int isSafe(int row, int col) {
int i, j;
// Check this row on the left side
for (i = 0; i < col; i++)
if (board[row][i])
return 0;
// Check upper diagonal on the left side
for (i = row, j = col; i >= 0 && j >= 0; i--, j--)
if (board[i][j])
return 0;
// Check lower diagonal on the left side
for (i = row, j = col; j >= 0 && i < N; i++, j--)
if (board[i][j])
return 0;
return 1;
}
// Recursive function to solve the N-Queen problem
int solveNQUtil(int col) {
if (col == N) {
printSolution();
return 1;
}
int row, res = 0;
for (row = 0; row < N; row++) {
if (isSafe(row, col)) {
board[row][col] = 1;
res = solveNQUtil(col + 1) || res;
board[row][col] = 0;
}
}
return res;
}
// Function to solve the N-Queen problem
void solveNQ() {
if (solveNQUtil(0) == 0)
printf("Solution does not exist");
}
int main() {
solveNQ();
return 0;
}
```

This program solves the **N-Queen problem using backtracking**. The goal is to place **N queens on an NxN chess board **so that no *two queens threaten each other*. In other words, no two queens should share the same row, column, or diagonal.

The program uses a recursive function

to place queens on the board one by one. The function tries all possible positions for a queen in the current column, and then recursively calls itself to solve the subproblem of placing the remaining queens. If a solution is found, the function returns 1 and prints the solution. If no solution is found, the function **solveNQUtil()****backtracks** and tries a different position for the queen in the current column.

The program also includes a

function to check if it is safe to place a queen at a given position on the board. This function checks the current row, column, and diagonals for any other queens.**isSafe()**

**Backtracking** is a powerful algorithmic technique that can solve many problems, but it can be slow for large problems due to the exponential search space. However, it is a useful technique to have in your toolkit as it can be used to solve many other problems, such as finding all possible paths in a maze or generating all permutations.