二維數組引用整個索引，而不是C中的單個單元格

Question

我似乎無法弄清楚我的問題是什麼。我正在編寫一個2D隨機遊走模擬，我的想法是使用二維數組來模擬它所在的網格。然而，在我的代碼中，當我嘗試引用數組中的特定單元格來增加它的值時，比如說bin [3] [4]，它會增加整個索引的值，即bin [1] [4]，bin [ 2] [4]，倉[3] [4]，等等。任何想法如何解決這個問題或我做錯了什麼？謝謝。

#include <stdio.h> 
#include <math.h> 

#define total 10. /*total iterations*/ 
#define walk 5 /*total # of steps in a walk*/ 
#define lambda 1.0 /*step size*/ 
#define binsize 0.1 
/*current chosen values are for bug checking simplicity*/ 

main() 
{ 
    float range = walk*lambda*2.; /*2 times max range, all positive*/ 
    int n,prob,i,k,j,placex,placey,bins; 
    double valuex,valuey, a; /*value starts at half range so all values are +*/ 
    bins=(range/binsize); 

    int bin[bins][bins]; 
    for(i=0;i<=bins;i++) /*zero out bin*/ 
    { 
    for(j=0;j<=bins;j++) 
    { 
     bin[i][j]=0; 
    } 
    } 

    for(k=0;k<total;k++) 
    { 
    valuex=range/2.; 
    valuey=range/2.; 

    for(n=1;n<=walk;n++) 
    { 
     prob= rand(4) % 100+1; 
     if(prob<=25) 
     { 
     valuex=valuex+pow(lambda,n); 
     } 
     else if(prob>25 && prob<=50) 
     { 
     valuex=valuex-pow(lambda,n); 
     } 
     else if(prob>50 && prob<=75) 
     { 
     valuey=valuey+pow(lambda,n); 
     } 
     else if(prob>75) 
     { 
     valuey=valuey-pow(lambda,n); 
     } 
    } 

    placex=floor(valuex/binsize+0.5); 
    placey=floor(valuey/binsize+0.5); 

    bin[placex][placey]=++bin[placex][placey]; 

    printf("%d %d %d\n",placex,placey,bin[placex][placey]); /* for bug checking. it prints the bin numbers where the value should go and then the value of that element.*/ 
    } 

    for(i=0;i<=bins;i++) 
    { 
    for(j=0;j<=bins;j++) 
    { 
     a=bin[i][j]/total; 
     //printf("%lf %lf %lf\n",i*binsize-range/2.,j*binsize-range/2.,a); /*format for input into IGOR*/ 
    } 
    } 
} 

Answer 1

想通了。你正在走出你的數組邊界。你的for循環上升到bin，但是數組的索引從0到bin -1。只要我在for循環中從< =中取出=就可以了。我的結束代碼看起來像這樣。通常走出數組邊界具有不可預知的行爲。

#include <stdio.h> 
#include <math.h> 

#define total 10. /*total iterations*/ 
#define walk 5 /*total # of steps in a walk*/ 
#define lambda 1.0 /*step size*/ 
#define binsize 0.1 
/*current chosen values are for bug checking simplicity*/ 

main()  { 
    float range = walk * lambda * 2.; /*2 times max range, all positive*/ 
    int n, prob, i, k, j, placex, placey, bins; 
    double valuex, valuey, a; /*value starts at half range so all values are +*/ 

    bins = (range/binsize); 

    int bin[bins][bins]; 

    /*zero out bin*/ 
    for(i = 0; i < bins; i++) { 
     for(j = 0; j < bins; j++) 
     bin[i][j] = 0; 
    } 

    for(k = 0; k < total; k++) { 
     valuex = range/2. - 1; 
     valuey = range/2. - 1; 

     for(n = 1; n <= walk; n++) { 
     prob = rand(4) % 100 + 1; 
     if(prob<=25) 
      valuex += pow(lambda, n); 
     else if(prob <= 50) 
      valuex -= pow(lambda, n); 
     else if(prob <= 75) 
      valuey += pow(lambda, n); 
     else 
      valuey -= pow(lambda, n); 
     } 

     placex = floor(valuex/binsize + 0.5); 
     placey = floor(valuey/binsize + 0.5); 
     bin[placex][placey] += 1; 

     printf("%d %d %d\n", placex, placey, bin[placex][placey]); /* for bug checking. it prints the bin numbers where the value should go and then the value of that element.*/ 
    } 

    for(i = 0; i < bins; i++) { 
    printf("\n"); 
     for(j = 0 ;j < bins; j++) { 
     if (bin[i][j] == 0) 
     printf(" "); 
     else 
     printf("%d ", bin[i][j]); 
     a = bin[i][j]/total; 

     } 
    } 
} 

我在底部添加的for循環只是輸出模式。