little q: illogical logical more c++

[T1001]

code below

diff_1 = 0;
	if (diff_1 == 0.00) {cout<<"flag_1";}
	if (diff_1==1.00) {pennies = pennies + 1;
	cout<<"increment by a penny to "<<pennies<<endl;}

diff_1 = 0;
	if (diff_1 == 0.00) {cout<<"flag_1";}
	if (diff_1==1.00) {pennies = pennies + 1;
	cout<<"increment by a penny to "<<pennies<<endl;}

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THis works a lot of the time but occasionally I'll run a number through the system and get bizzare output:

put in for diff_1-->1.00 (that's all - no decision tress)

sometimes 1.00 bypasses both conditions even though I manually set diff_1 to 1.00. and also fails to execute the decision tree next to it:

if (diff_1==1.00) {pennies = pennies + 1;
	cout<<"increment by a penny to "<<pennies<<endl;}

if (diff_1==1.00) {pennies = pennies + 1;
	cout<<"increment by a penny to "<<pennies<<endl;}

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