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2-D Arrays

2-D Arrays. Declaration & Initialization. Declaration. You can think of 2D arrays as a matrix rows and columns: a 4x3 matrix 2 5 4 1 3 7 6 2 1 9 8 0 4 rows and 3 columns int x[4][3];. Declaration and Initialization.

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2-D Arrays

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  1. 2-D Arrays Declaration & Initialization

  2. Declaration • You can think of 2D arrays as a matrix rows and columns: • a 4x3 matrix 2 5 4 1 3 7 6 2 1 9 8 0 • 4 rows and 3 columns • int x[4][3];

  3. Declaration and Initialization int x[4][3] = {{1, 2, 4}, {2, 3, 5}, {1, 4, 2}, {4, 3, 1}}; • x[1][2]  ? • x[3][1]  ? • ? • ? int x[][3] = {{1, 2, 4}, {2, 3, 5}, {1, 4, 2}, {4, 3, 1}}; int x[4][3] = {1, 2, 4, 2, 3, 5, 1, 4, 2, 4, 3, 1}; int x[][3] = {1, 2, 4, 2, 3, 5, 1, 4, 2, 4, 3, 1}; int x[4][3] = {1, 2, 4, 2, 3, 5, 1, 4}; int x[4][3] = {{1, 2, 4}, {2, 3, 5}, {1, 4, 0}, {0, 0, 0}};

  4. Filling a 2d array for(i=0; i<rows; i++) { for(j=0; j<cols; j++) { x[i][j] = rand()%10; } }

  5. Survey • A survey has 15 questions and each question has 5 answers. The survey results are in a file called Survey.txt in the following format: 1 4 5 3 5 3 4 5 1 1 2 3 2 4 5 4 3 2 4 3 4 5 1 2 3 2 2 4 3 1 1 2 3 2 3 4 3 4 5 3 4 2 1 2 5 … • Read each survey result into an array • How many people surveyed? Number of lines (Nlines). • How many questions in each survey? Number of columns = 15 (Nquest) • How many different values for each question? 5 (Nvalue) • Need to use two dimensional array • intSrvy[Nlines][Nquest] • What is the value of Srvy[2][10]?

  6. Survey Sz=--i; /* Print array */ for(i=0; i<Sz; i++) { for(j=0; j<NQUEST; j++) printf("%d ", Sarr[i][j]); printf("\n"); } fclose(flp); return(0); } • #include <stdio.h> • #define NLINES 100 • #define NQUEST 15 • int main(void) { • FILE*flp; • intSarr[NLINES][NQUEST] = {0}; • inti, j; • intStatus=1, Sz; • flp = fopen("Survey.txt", "r"); • /* Fill array */ • i=0; • while(Status != EOF) { • for(j=0;j<NQUEST;j++) { • Status = fscanf(flp, "%d", &Sarr[i][j]); • if(Status == EOF) break; • } • i++; • }

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