Can someone explain the misbehaviour of this code

[jinnejeevansai]

I was trying to solve a problem but the problem is the string a is disappearing at the end of for loop.

#include<stdio.h>
#include<string.h>
int main()
{
        int i,t,j;
        char a[10],b[10];
        scanf("%d",&t);
        for(i=0;i<t;i++)
        {
                int c=0;
                scanf("%s %s",a,b);
 
                for(j=0;j<strlen(a);j++)
                {        
                        printf("%s",a);\\printing string here gives the string 
                        if((a[j]=!b[j])&&(a[j]!='?')&&(b[j]!='?'))
                        {
                                printf("No\n");
                                break;
                        }
                        else
                        {
                                c++;
                        }
                       printf("%s",a);\\printing here is not giving the string
                }
              if(c==strlen(a))
                printf("Yes\n");
        }
}
 
 
 
 

[weaknessforcats]

Check this line of code:

if((a[j]=!b[j])&&(a[j]!='?')&&(b[j]!='?'))
 

There is no =! operator. You meant to use !=. That =! will act as an assignment operator and will assign !b[j] to a[j].

Every time b[j] is true (not zero), then zero will be assigned to a[j]. That assigned zero will act as a null terminator making your string disappear.