View Compilation Error

0_0_34879705_21305.cpp: In function 'int main()':
0_0_34879705_21305.cpp:8:19: error: 'strlen' was not declared in this scope
 for(i=1;i<strlen(a);i++)
                   ^
0_0_34879705_21305.cpp:14:19: error: 'strlen' was not declared in this scope
 for(j=0;j<strlen(a);j++)
                   ^