View Compilation Error

0_0_30077462_5832.cpp: In function 'int main()':
0_0_30077462_5832.cpp:15:21: error: 'strlen' was not declared in this scope
   int t1=strlen(str1),t2=strlen(str2);
                     ^
0_0_30077462_5832.cpp:18:24: error: 't2' was not declared in this scope
   for(int j=0,k=t1/2;j<t2;j++,k++)
                        ^
0_0_30077462_5832.cpp:20:7: error: 'i' was not declared in this scope
   for(i=t1/2,k=t2+t1/2;i<t1;i++,k++)
       ^
0_0_30077462_5832.cpp:20:14: error: 'k' was not declared in this scope
   for(i=t1/2,k=t2+t1/2;i<t1;i++,k++)
              ^
0_0_30077462_5832.cpp:20:16: error: 't2' was not declared in this scope
   for(i=t1/2,k=t2+t1/2;i<t1;i++,k++)
                ^
0_0_30077462_5832.cpp:22:8: error: 'k' was not declared in this scope
   str3[k]='\0';
        ^