Use of conditions in matrices

Question

I need to do a program that reads a 4X4 matrix and then sums the values in each row and then for each column. I’m not sure how to define my condition.

#include <stdio.h>

int main()
{
int valores[4][4];
int i,j, somacol, somalin;

for(i=0; i<4; i++){
      for(j=0; j<4; j++){
printf("Informe os valores:", i+1, j+1);
scanf("%d", &valores[i][j]);
}
}
for(i=0; i<4; i++){                     
     for(j=0; j<4; j++){
printf("%d\t", valores[i][j]);
}
printf("\n");
}
for(i=0; i<4; i++){
     for(j=0; j<4; j++){
 somalin=valores[i][j];
 }
 }
 for(i=0; i<4; i++){
 for(j=0; j<4; j++){
 somacol=valores[i][j];
 }

Answer 1

Actually you need four somalin and four somacol, one for each row/column in valores.

So once you popular the matrix, you will make a for double to address each element and increment the sum of the respective row and column.

Step by step:

#include <stdio.h>

int
main(int argc, char ** argv) {
    int valores[4][4];
    int i, j, somacol[4], somalin[4];

First we get the values. Here you do it with printf()and scanf(), but it may suit you to isolate this functionality in a function so that later you want to get these values from a file or something like that.

    for (i = 0; i < 4; i ++) {
        for (j = 0; j < 4; j ++) {

When it’s time to call printf() and friends, remember to put the format specifier (%d in this case); otherwise none of the dynamic values you want to show.

            printf("Informe os valores (%d, %d): ", i + 1, j + 1);

As to the scanf() and so, remember to always start string format with a blank space for it to "eat" the return car you gave the previous time that called scanf(). In addition, as the matrix is int, must pass the address of the matrix element (with the operator &):

            scanf(" %d", &(valores[i][j]));
        }
    }

Then we start all the somalin and somacol to zero so we can use them with the increment operator +=.

    for (i = 0; i < 4; i ++) {
        somalin[i] = somacol[i] = 0;
    }

Now comes the part that matters: for double so that in the body of the second for, we have the indices of one of the sixteen elements of valores. Just increment the sum of the row and column corresponding to that element:

    for (i = 0; i < 4; i ++) {
        for (j = 0; j < 4; j ++) {
            somalin[i] += valores[i][j];
            somacol[j] += valores[i][j];
        }
    }

After that, just do anything with the values and return. If you are doing this on main(), remember that she returns int and give a return 0; before leaving. Good manners.

    for (i = 0; i < 4; i ++) {
        printf("Soma da %dª linha: %d\tSoma da %dª coluna: %d\n", i + 1, somalin[i], i + 1, somacol[i]);
    }

    return 0;
}

Answer 2

#include <stdio.h>

int main() {
    int valores[4][4];
    int i, j, soma;
    
    for(i = 0; i < 4; i++) {
        for(j = 0; j < 4; j++){
            printf("Informe os valores de [%d, %d]:\n", i + 1, j + 1);
            scanf("%d", &valores[i][j]);
        }
    }
    for(i = 0; i < 4; i++) {                     
        for(j = 0; j < 4; j++) {
            printf("%d\t", valores[i][j]);
        }
        printf("\n");
    }
    for(i = 0; i < 4; i++) {
        soma = 0;
        for(j = 0; j < 4; j++){
            soma += valores[i][j];
        }
        printf("Soma da linha %d: %d\n", i + 1, soma);
    }
    for(i = 0; i < 4; i++) {
        soma = 0;
        for(j = 0; j < 4; j++){
            soma += valores[j][i];
        }
        printf("Soma da coluna %d: %d\n", i + 1, soma);
    }
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

There is no mistake in the condition.

I gave an organized in the code because it helps to understand what is happening.

The whole sum logic was incorrect. It did not restart the sum variable (which may be the same) in each row/column change. And it wasn’t printing when finished every sum.

It wasn’t actually adding up, but it was replacing the value in each pass.

Note that in the first loop I used [i][j] because you need to take each row and then each column of it. In the second I used [j][i] because I need to take every column and then every row of it.