Why does the code generate garbage at the beginning of the vector?

Question

the following code generates an unexpected result, at the end of the loop the first positions of the vector are with stored garbage, someone can tell why this is happening, and where is the error?

OBS. The code has the same behavior in both C and C++ (gcc and g compilers++)

Code:

    #include<stdio.h>
    #include<stdlib.h>


    int V = 10;
    int E = 20;

    int main() {
        double sol[3*E + V];
        int ind[3*E + V];
        double val[3*E + V];
        double ub[3*E + V];
        double obj[3*E + V];
        char **varname;
        char vtype[V];
        int erro;


        varname = (char**) malloc((3*E+V)*sizeof(char**));

        for (int i = 0; i < V; ++i) {
            obj[i] = 0;
            vtype[i] = 'B';
            ub[i] = 1;
            varname[i] = (char*) malloc(sizeof(char*)*10);
            sprintf(varname[i], "y_%i", i);
        }

        int k = 0;
        for (int i=V; i < (V+3*E); i+=3) {
            for(int j=0; j < 3; ++j) {
                obj[i+j] = 0;
                vtype[i+j] = 'B';
                ub[i+j] = 1;
                varname[i+j] = (char*) malloc(sizeof(char*)*15);
                sprintf(varname[i+j], "x_%i_%i_%i", 0, 0, j);
            }
            k++;
        }

        for (int i=0; i < (V+3*E); ++i) {
            printf(" obj[%d]: %.1f \t(%s), \t (%c) <= (%.1f)\n", i, obj[i], varname[i], vtype[i], ub[i]);
        }

        getchar();

    }

Exit:

    Success time: 0 memory: 2296 signal:0
     obj[0]: 156842099844.5     (y_0),   (B) <= (1.0)
     obj[1]: 156842099844.5     (y_1),   (B) <= (1.0)
     obj[2]: 156842099844.5     (y_2),   (B) <= (1.0)
     obj[3]: 156842099844.5     (y_3),   (B) <= (1.0)
     obj[4]: 156842099844.5     (y_4),   (B) <= (1.0)
     obj[5]: 156842099844.5     (y_5),   (B) <= (1.0)
     obj[6]: 0.0    (y_6),   (B) <= (1.0)
     obj[7]: 0.0    (y_7),   (B) <= (1.0)
     obj[8]: 0.0    (y_8),   (B) <= (1.0)
     obj[9]: 0.0    (y_9),   (B) <= (1.0)
     obj[10]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[11]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[12]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[13]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[14]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[15]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[16]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[17]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[18]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[19]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[20]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[21]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[22]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[23]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[24]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[25]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[26]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[27]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[28]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[29]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[30]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[31]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[32]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[33]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[34]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[35]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[36]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[37]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[38]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[39]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[40]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[41]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[42]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[43]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[44]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[45]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[46]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[47]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[48]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[49]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[50]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[51]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[52]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[53]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[54]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[55]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[56]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[57]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[58]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[59]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[60]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[61]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[62]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[63]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[64]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[65]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[66]: 0.0   (x_0_0_2),   (B) <= (1.0)
     obj[67]: 0.0   (x_0_0_0),   (B) <= (1.0)
     obj[68]: 0.0   (x_0_0_1),   (B) <= (1.0)
     obj[69]: 0.0   (x_0_0_2),   (B) <= (1.0)

Hugs!

Answer 1

Your array vtype is only size 10, but you write on it like it’s the same size as the others. The way local variables are structured, you end up writing over the memory of other arrays. In this case you are typing over the array obj, what ends up generating the garbage that you observed.