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Repetition is the best method for memory; spend one minute each day to remember the basics of C language.

“Series of 100 Essential Knowledge Points for C Language Beginners“

31. Tips for Using Nested Loops: Applications of Multiple Loops

1. Basic Concept of Nested Loops

A nested loop refers to a complete loop structure contained within another loop body, forming multiple layers of loops:

for (initialization; condition; iteration) {       // Outer loop
    for (initialization; condition; iteration) {   // Inner loop
        // Loop body code
    }
}

2. Typical Applications

1. Processing Two-Dimensional Arrays

int matrix[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
for (int i = 0; i < 3; i++) {          // Row loop
    for (int j = 0; j < 3; j++) {      // Column loop
        printf("%d ", matrix[i][j]);
    }
    printf("\n");
}

2. Matrix Operations

// Matrix multiplication
for (int i = 0; i < rowsA; i++) {
    for (int j = 0; j < colsB; j++) {
        int sum = 0;
        for (int k = 0; k < colsA; k++) {
            sum += A[i][k] * B[k][j];
        }
        C[i][j] = sum;
    }
}

3. Tips for Using Nested Loops

1. Use Different Loop Variables

for (int i = 0; i < 5; i++) {      // Outer loop uses i
    for (int j = 0; j < 3; j++) {   // Inner loop uses j
        printf("%d-%d ", i, j);
    }
}

2. Control the Depth of Nesting

// It is recommended to limit to a maximum of 3 levels of nesting
for (int i...) {
    for (int j...) {
        for (int k...) {
            // If more than 3 levels, consider refactoring
        }
    }
}

3. Exit Nested Loops Early

int found = 0;
for (int i = 0; i < n && !found; i++) {
    for (int j = 0; j < m && !found; j++) {
        if (arr[i][j] == target) {
            found = 1;
            break;
        }
    }
}

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