Compilare: user.cpp: In function ‘int main()’: user.cpp:17:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a[1]);i++) ^ user.cpp:18:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<strlen(a[2]);j++) ^ user.cpp:35:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<strlen(a[1]);i++) ^ user.cpp:36:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(j=0;j<strlen(a[2]);j++) ^ user.cpp:37:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(h=0;h<strlen(a[3]);h++) ^ user.cpp:39:35: warning: suggest parentheses around comparison in operand of ‘==’ [-Wparentheses] if(a[1][i]==a[2][j]==a[3][h]) { ^