/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
  printf("Entrer deux equation\n");
  ^~~~~~
/in/foo.c:4:2: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:4:2: note: include '<stdio.h>' or provide a declaration of 'printf'
/in/foo.c:7:3: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
   scanf("%f", &a[i][j]);
   ^~~~~
/in/foo.c:7:3: warning: incompatible implicit declaration of built-in function 'scanf'
/in/foo.c:7:3: note: include '<stdio.h>' or provide a declaration of 'scanf'