value over written in the array during loop-CodePudding

I am currently trying to convert an equation into simpler form and found out that my codes are over writing the value at the end of the loop.

I have found out similar discussions but not exactly what I am looking for. Most of articles were using other languages so I couldn't get the answer.

Any answers are appreciated and thanks in advance.

followings are my code

int index = 0;
int result = 0;
char tresult[100];
char *equation[100] = { NULL, };
char *temp = strtok(input, " ");

for(int i = 1; i < x; i = i   2)
{
    char *temp_sign = equation[i];
    
    if(*temp_sign == '*')
    {
        result = atoi(equation[i - 1]) * atoi(equation[i  1]);
        sprintf(tresult, "%d", result);
        equation[i - 1] = tresult;
        sprintf(equation[i], "%d", 0);
        sprintf(equation[i   1], "%d", 0);
    }
}

for(int j = 0; j < x; j  )
{
    printf("%s ", equation[j]);
}

Expected input

5 * 3   1 * 2

targeted output

15 0 0   2 0 0

I will remove 0 by adding extra codes to make it as

15   2

but currently, my output looks like

2 0 0   2 0 0

When I print out the value in the loop, all the values were correctly shown. What may be the cause of such problem?

CodePudding user response：

It might be easier to understand if we draw out the pointer instead.

Assuming that input is initially equal to "5 * 3 1 * 2", then after the loop equation will look something like this:

 ------------- 
| equation[0] | ------------------------\
 -------------                          |
| equation[1] | --> | input[2] | ... |  |      ------------ ----- 
 -------------                           >--> | tresult[0] | ... |
| equation[2] | --> | input[4] | ... |  |      ------------ ----- 
 -------------                          |
| equation[3] | ------------------------/
 ------------- 
| equation[4] | --> | input[10] | ... |
 ------------- 
| equation[5] | --> | input[12] | ... |
 -------------

As seen in the above "drawing" both equation[0] and equation[3] will be pointing to the first character of the single array tresult.

And tresult will always contain the contents last written into it with sprintf(tresult, "%d", result). Which in your example will be "2".