How to declare doubles inside a matrix (2d arrays) in C?

user_10906383 0
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I am learning by myself (started few days ago) and could not find reliable information in portuguese (my home language). After just too much headache, I gave up and came here for help. I do not know how to make am array/2d array of doubles, only intergers. The following code works as expected:

int main(void){    
int matriz[5][2] =  {{1,2},  // DECLARATION OF MATRIX COMPOSED OF INTERGERS
                     {3,4},
                     {5,6},
                     {7,8},
                     {9,10}};
int maior = matriz[0][0];   // BIGGEST NUMBER INSIDE MATRIX, STARTED AS FIRST POSITION
int soma = 0;               // SUM OF NUMBERS START WITH ZERO
int lin = 0;                // INDICATION OF LINE
int col = 0;                // INDICATION OF COLUMN
for (lin = 0; lin < 5; lin++){
    for (col = 0; col < 2; col++){
    if (maior < matriz[lin][col]) {maior = matriz[lin][col];}
    soma += matriz[lin][col];
    }   
}
printf("A soma dos numeros eh %d e o maior numero eh %d\n", soma, maior); 
// THE SUM OF NUMBERS IS %D AND THE BIGGEST NUMBER IS %D
// I COPIED THE FOLLOWING CODE FROM ELSEWHERE TO SEE WHAT WAS GOING ON
    int i, j;
    for ( i = 0; i < 5; i++ ) {
          for ( j = 0; j < 2; j++ ) {
         printf("a[%d][%d] = %d\n", i,j, matriz[i][j] );
      }
   }
return 0;}

The output is just as expected:

A soma dos numeros eh 55 e o maior numero eh 10
a[0][0] = 1 
a[0][1] = 2 
a[1][0] = 3 
a[1][1] = 4 
a[2][0] = 5 
a[2][1] = 6 
a[3][0] = 7 
a[3][1] = 8
a[4][0] = 9
a[4][1] = 10

**

However any change as the folowing code is always wrong:

**

int main(void){
double matriz2[5][2] = {{10000,1000},
                        {100,10},
                        {1,0.1},
                        {0.01,0.001},
                        {0.0001,0.00001}};
double maior2 = matriz2[0][0];
double soma2 = 0;
int lin2 = 0;
int col2 = 0;
for (lin2 = 0; lin2 < 5; lin2++){
    for (col2 = 0; col2 < 2; col2++){
    if (maior2 < matriz2[lin2][col2]) {maior2 = matriz2[lin2][col2];}
    soma2 += matriz2[lin2][col2];
    }   
}
printf("A soma dos numeros eh %d e o maior numero eh %d\n", soma2, maior2);

for ( i = 0; i < 5; i++ ) {
      for ( j = 0; j < 2; j++ ) {
         printf("a[%d][%d] = %d\n", i,j, matriz2[i][j] );
      }
   }
return 0;}

The output is always wrong as I keep changing it. I declared long doubles, doubles, interger and doubles etc. And each time the code outputs wrong answers. Some combinations output negative numbers. Others just output ZERO everywhere. Two examples: 

A soma dos numeros eh 0 e o maior numero eh 0
a[0][0] = 10000
a[0][1] = 1000
a[1][0] = 100
a[1][1] = 10
a[2][0] = 1
a[2][1] = 0
a[3][0] = 0
a[3][1] = 0
a[4][0] = 0
a[4][1] = 0

or 

A soma dos numeros eh 953826337 e o maior numero eh 0
a[0][0] = 0
a[0][1] = 0
a[1][0] = 0
a[1][1] = 0
a[2][0] = 0
a[2][1] = -1717986918
a[3][0] = 1202590843
a[3][1] = -755914244
a[4][0] = -350469331
a[4][1] = -1998362383

I simply could not find a way to declare or put double number in a matrix. How can I do it?

declaration matrix c
2 Answers

%d format specifier of printf expects an int argument, but you are passing a double. Your program then exhibits undefined behavior. Consult your favorite C or C++ textbook on how to output a value of type double.

user_16701290

You have tagged both C & C++ you should pick one or the other. I'll give answers for both languages.

If using C with printf() when you change your 2D array from int to double the calculations appear to be fine, what is wrong here is your output with printf(). You are using %d which expects an int but you are passing it a double and this leads to undefined behavior. When using float or double change this to %f or %g.

If using C++ try not to use printf(). Instead you should include iostream. Then your output would look something like:

// printf("A soma dos numeros eh %d e o maior numero eh %d\n", soma2, maior2);
std::cout << "A soma dos numerous eh " << soma2 << " e o maior numero eh << maior2 << '\n';

for ( i = 0; i < 5; i++ ) {
    for ( j = 0; j < 2; j++ ) {
        // printf("a[%d][%d] = %d\n", i,j, matriz2[i][j] );
        std::cout << "a[" << i << "][" << j "] = " << matriz2[i][j] << '\n';
    }
}
user_17578050
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