encountered strange situation-variable value - c

Question

I am programming on some device and I encountered
rather strange situation.
The same variable - for the first time has correct value,
but the SAME variable on a different place in code,
has a DIFFERENT value.
What can be causing this? I am pretty sure I didn't modify
the variable in between, I am also pretty sure I didn't
modify the variable using some pointers accidentally.
What can be causing this? I am really confused?
Can it be related that I for example used whole available stack
space of some function - and because of this compiler automatically
0-ifies my variable(or something similar)?
I have some long code inside a single function f.
Here's whole details on usage of pointsEntered variable in my code (how it is used).
/* Let the user input points */
s32 pointsEntered = 0;
int pointsCounter = 0;
while(1)
{
if(pointsCounter == 3)
return; // User entered wrong points 3 times, exit function
bool retStatus = false;
retStatus = inputPoints(&pointsEntered);
if(false == retStatus) // If user didn't enter amount, exit this function
return;
if(pointsEntered>atoi(userAmount)){
PromptBox(false, 0, "Points should not be more\n than current points");
pointsCounter++;
continue;
}
break;
}
// PROBLEM: pointsEntered - is OK here but as it will be shown below, it gets modified down the way
// even though I don't change it directly
char intTest1[50];
sprintf(intTest1, "1pentered %d", pointsEntered); // Here the value is OK! It shows value that I entered, e.g., 220
PromptBox(false, 0, intTest1);
/* Let the user enter 4 digit pin code */
u8 pinEntered[5] = {0};
bool retStatus1 = false;
retStatus1 = inputPin(pinEntered);
pinEntered[5]='\0';
if(false == retStatus1) // If user didn't enter amount, exit this function
return;
char intTest2[50];
sprintf(intTest2, "2pentered %d", pointsEntered); // Here pointsEnetered is OK
PromptBox(false, 0, intTest2);
/* Compute hash of pin code*/
s32 siRet1 = 0;
u8 pinVerify[25]={0};
u8 hashResult[16] = {0};
memcpy(pinVerify,pinEntered,4);
memcpy(&pinVerify[4],"XXXX",21);
siRet1 = sdkMD5(hashResult,pinVerify,25);
char intTest3[50];
sprintf(intTest3, "3pentered %d", pointsEntered); // Here pointsEntered has changed!!!
PromptBox(false, 0, intTest3);
/* convert string hash code to byte array */
unsigned char val[16] = {0};
unsigned char * pos = pinHash;
size_t count = 0;
// WARNING: no sanitization or error-checking whatsoever
for(count = 0; count < sizeof(val)/sizeof(val[0]); count++)
{
sscanf(pos, "%2hhx", &val[count]);
pos += 2 * sizeof(char);
}
char intTest4[50];
sprintf(intTest4, "4pentered %d", pointsEntered);
PromptBox(false, 0, intTest4);
/* Does the pin hash match ? */
if (siRet == SDK_OK && (!memcmp(hashResult,val,16)))
{
MsgBox("PIN OK","",0,SDK_KEY_MASK_ESC | SDK_KEY_MASK_ENTER);
}
else
{
MsgBox("PIN doesn't match-exiting","",0,SDK_KEY_MASK_ESC | SDK_KEY_MASK_ENTER);
return;
}
char intTest[50];
sprintf(intTest, "pentered %d", pointsEntered);
PromptBox(false, 0, intTest);

Answer 1

These two lines may cause it (as it's undefined behavior):
u8 pinEntered[5] = {0};
...
pinEntered[5]='\0';
Here you declare an array of five entries, but then you assign to a sixth item. This will most likely overwrite any previous variable on the stack.